They need to find a way to make this thing appealing to non-Shenmue fans. Just get out there and say "you don't have to play older titles to enjoy this, this game is accessible for all types of players". I'm sure they've said something to that effect already, but they really need to drive it home if they want to reach a wider audience. As it is, I bet most of the hardcore Shenmue fanbase has already backed the project.
Also, physical PS4 copy. I'll back it as soon as they add that as a reward tier. If not, I'll settle for a digital copy, but a physical version for consoles would definitely bring in more backers. I don't know why Sony hasn't already agreed to this.
This is a huge issue as well, a lot of people asking Yu for 1+2 HD.
The problem is though: SEGA is responsible for both games. Not only that they are having a different focus right now but there is also the license issues.
Shenmue 2 was on the dev XBLA once as 'Project Barkley' and part of that huge SEGA DC-remaster wave that gave us Crazy Taxi, NiGHTS and few others. I assume that Shenmue 2 HD is probably already done, but they couldn't release it back then because of those licensing problems and can't do it now.
I have no idea how much a social media campaign would do, but chances seem to be very grim. I think SEGA is well aware of Shenmue's following and would have gave them at least the Shenmue 2 remaster, but this seems impossible.
As for Shenmue 1: I saw a rumor once that said that both games are HD ready to be released on XBLA back then, but that SEGA held them back. Dunno, I can see them having planned to release Shenmue 2 only since that was a orginal Xbox game once and had a Shenmue 1 video recap on disc.
To be honest: I think if they went out on that Sony stage that day, announced the Shenmue 3 Kickstarter AND announced a Shenmue 1+2 HD on PSN available right out of the door, it would have pushed the KS a lot. Imagine Shenmue 1+2 HD having just very simple features like screenshot with #PS4Share tags; people would have spread word on the game themselves that way and I bet some scenes could have turned into memes and spread it even further.
As of right now, I'm happy that this exists in some way, even though I think the Kickstarter and organization of everything could have been smoother and more professional. I'm very annoyed by the false info spreaded by a jaded vocal minority on the internet to create a certain narrative, but you know what? Fuck them. This is bigger than they could ever be.