SEGA technically has the assets to launch a new system. There's enough Sonic fans out there to do it. Add Atlus, among others you could feasibly have enough of a userbase to have a strong launch. If SEGA had a proper management that would be able to utilise what they got. Maintaining it though and adding new users to buy the system after the launch year is the issue.
The problem with this type of debate is reality and people ignoring that reality because they have little to no understanding on what SEGA is today.
1. Its not up to SEGA whether they want a new system, its up to Sammy who actually OWNS SEGA.
Sammy management that runs SegaSammy have no interest in making home console systems. Believe it or not, this topic actually came up within five years into the SEGASammy era, when what was left of the old guard at SEGA lobbied Sammy to let them go back into the console business. This was when, thanks to the panchinko/pachislot money, Sammy was throwing their cash around which they invested into letting SEGA europe buy The Creative Assembly as well as SEGA of america make all its contract deals and buying expensive licenses like Marvel and Alien or the PG deal. The result was the old stalwarts left SEGA or were fired depending who you talk to after Sammy refused. The president of SEGA of america at the time got backlash from fans because he mentioned this in a interview as well as the fact Yu Suzuki was no longer at the company. As long as sammy is in control, as well as the stockholders there will not be a new SEGA system.
2. Many of the people who could have created a new system are not in SEGA.
When SEGA scrapped the DC, a lot of the factories that SEGA owned that mass produced the system, including previous systems and hardware, were mostly closed down. The ones that weren't were the ones involved in arcade manufacturing and they are no longer what they use to be either. Financially in order to produce a new system, SEGA not only has to spend on R+D but they have to invest in manufacturing and the staff needed to do it. Then on top of that, the main console designers aren't there anymore. None of the current staff have engineering experience and hasn't worked in a culture where hardware was prominent in SEGA. So even if they did return the system will not be as SEGA as people would want it to be.
3. The SEGA fanbase.
The SEGA fanbase is not what it was back in the 90s and half of it is SEGA's fault. SEGA does not have a united fanbase like Sony and Nintendo has. Even capcom. The issue SEGA has and what they are trying to fix, is that what SEGA has at the moment are fans of games they PUBLISH and not fans of th SEGA brand. A sony fan or nintendo fan is most likely going to buy any type of first party game they will put out. Even if the customer is not a fan of a game genre that these companies make, they would try it because they are fans of the brand and all that comes with it. Thats what makes or break a successful new IP launch for these companies. That use to be the same for SEGA when they were a console producer. But SEGA screwed it up. The first and continuing screw up is the fracturing between fanbases between people who were fans of SEGA's arcade games and people who were fans of SEGA game consoles. During the saturn era and earlier in the genesis era, SEGA started to keep certain games as arcade exclusives and not port them. This continued into the saturn era and the DC era and became a glaring hole in their current third party era. Without regular ports it kept SEGA from gaining new arcade fans while the arcade fanbase had little to no interest in buying a system for a game that SEGA was updating in the arcades regularly anyway. Especially when those games didnt have a port. So when you have a fractured fanbase divided by two platforms(added by other circumstances like what happened to the arcade market in the west) and your not doing anything to bring them together(by not porting the game people want) you leave money on the table to a degree.
The second mistake was SEGA's failure to maintain and grow its console userbase after the Dreamcast. When SEGA went third party not all of their fanbase went with them. Half of them quit since they couldnt fathom playing a SEGA game on a non SEGA system. To them including myself, we believed SEGA had the best hardware, SEGA been making consoles as far as many of us could remember. And now SEGA is dropping hardware and making games for companies that tried to put it out of business? There was no way any of those guys were going to buy a nintendo system to play SEGA games. EVER. The PS2 situation was that many SEGA fans blamed sony for the DC's demise and the news that VIRTUA FIGHTER 4 would be a PS2 exclusive was the straw that broke the camel's back. Add to the fact that the DC was a great system with great games and which had won many SEGA fans back to the company after the western Saturn fiasco and their experience in gaming up to that point was whoever had the best games usually had success. But that didn't happen this time. To them it was no longer a gamers world it had become dominated by casuals who thought sony created video games. So they either quit gaming altogether, some migrated to PC gaming, some went to what was left of the arcades. The fans that did stay behind went with the Xbox because they thought SEGA would be strongly supporting it. When they didn't, that was it. While SEGA had success on PS2 and gamecube, it wasn't driven by actual SEGA fans but by people who never played or had limited experience with SEGA. Because a lot of the SEGA dev studios were allowed to pick and choose which system they wanted to make games for, and not follow an all platform for key game franchises that companies like capcom sometimes favoured, they lost a lot of fans who were into the SEGA brand.
This leads to the current situation. A lot of the people buying SEGA games today are not SEGA fans but are fans of certain games that SEGA publishes. There is little to no cross over as these fans only buy these games they are a fan of from SEGA. They wouldn't buy a brand new title from them. Which is why (partially) games like Binary Domain flopped and most other attempts to launch new IP has stalled. Sonic fans are only interested in Sonic. Most of the sonic fanbase today were nintendo gamers who brought Sonic when it first appeared on gamecube the GBA and then the Wii and NDS. The SEGA acquired Total War and Football Manager titles and the fanbase they have will only buy those titles and less likely would buy a SEGA game (for various reasons). Like A Dragon may be different but from i've seen a lot of the newer fans that joined in are just in for that series. Atlus doesnt have this problem because they have managed to maintain and grow their userbase where you can see the growth of their franchises, some of which were never million unit sellers, now reach that point or launch a successful launch of a new IP. Where SEGA failed was to ensure that any game, new and old was collectilvy branded under the SEGA brand and fully integrated especially the fanbases that these games have. A complete opposite on what tookplace during the Genesis era where games not even made by SEGA are still remembered as being SEGA.
As for the nostalgia SEGA fans or claim to be one, the reality is there's not enough of you around. We haven't been sustaining the company during the SEGAsammy era. The idea that SEGA is making a return to satisfy us, is delusional. They not. They trying to get new customers into the brand. Thats why JSR and Crazy Taxi will be GAAS style titles. That's why VF has been rebranded and going in the direction they going in. That's why they haven't bothered to return Phantasy Star to what it was in the 90s. The difference is, they not marketing these upcoming games as their own thing but under the banner of SEGA.
So even if SEGA launched a SEGA system, how many of these fans today would buy it and not just stick with the company hardware producer they really are a fan of? This new era strategy from SEGA is their attempt to address that, most likely trying to create new fans for the brand who will be fans of the brand and securing at least cross game pollination where they would buy a new IP from SEGA which the current userbase doesnt in large numbers.