I don't know. I think the most important thing is to make the case for the handheld against cell phones in Japan and/or to make the case for the home console as a second console in the west. The thing is, a Nintendo console is very much in demand as far as I am concerned and I am not an engineer on the cutting edge of technology so I have no idea as to how to accomplish these things. Price, launch year momentum, gimmick, messaging, and the market environment will all be tremendously important.
So hopeful speculation:
As to hardware: My 'realistic' hope, which is mostly backwards looking but also based on GAF speculation groupthink, is that it will be a power efficient home console with parts that accomplish PS4/XBOne ballpark results in a cooler (temperature), more modern way. There will be some idiosyncrasies, partly due to cross compatibility with a handheld console (say, ARM vs x86) and partly due to Nintendo (say, strange RAM), but nothing too exotic to prevent ports (and if it moves decent numbers in the west, it'll get the biggest EA/Acti/Ubi games again). It will not have backwards compatibility, but key Wii U games with a far off sequel will be ported to it a la BotW and it will have virtual console support through to at least GCN (as well as Wii, depending on the gimmick). I don't know how expensive this sounds so far, but I imagine Nintendo is shooting for something between $199 and $299.
As to cross-compatibility: the machine will use 'cartridges' and share most of its games with a handheld unit either launched concurrently or within the first year, year and a half of the home units launch (I'm hoping it comes out sooner rather than later--especially in Japan). Retail games will be priced between, say, $19.99 and $59.99 depending on size and scope of development instead of system. I'm assuming that there will be no mandate that all games for the home console must also work on the handheld, but every retail game that works on the handheld will work on the home console (perhaps without large performance bonuses though, like a Super Gameboy). Many of the games will be at previously 'handheld' pricing and be lower budget Nintendo and Japanese third party games. Nintendo will continue its current push towards indie content for its eShop and at least its own 'phone' games will be available on the handheld, which will have some sort of touch control capability. Perhaps the home controller will too. The VC will, perhaps, be more limited on the handheld, maybe only getting up to N64. Most importantly, eShop games that support both consoles will be crossbuy, like the cartridges. The VC will, however, be once again a fresh start from the Wii U and 3DS but will finally be forward compatible and will have crossbuy where applicable.
As to early software: The NX will launch with BotW, Smash NX, Pikmin 4, and Luigi's Mansion NX as the largest Nintendo offerings in the launch weeks. Retro's game will come either summer 2017 or close out the year in Feb/Mar/April 2018. Mario NX will be the holiday game for 2017. Splatoon 2 and MK9 will be out by Mar 2019. NX will see DQ X and XI (the PS4 version) and FFXV as well as the support 3DS received, most notably Monster Hunter. Nintendo will try and keep Level 5 on board despite the latter's increasing pivot to mobile; they will get the bigger games as mobile/NX releases.
As to gimmick: ?????? Will there be one? Will Motion controls return? This is perhaps the biggest thing that could potentially tank the system by not allowing for decent specs or low cost and it could also be what sells the system in a Wii like situation. And I have no idea what to even hope Nintendo will do in this regard.