So, I get the appeal of doing something like this, but I can't help but to wonder if the N64 would be possible? Talk about challenge, there STILL to this day isn't a truely compatible N64 emulator available. I mean for God's sake look at the progress CEMU (WiiU Emu) has had in just months of development, yet still no "good" n64 after 20 years?!
I know you are friends with Marshall from Retroactive who already has a wealth of N64 know-how, and infact I imagine that a N64 fpga with hdmi output alone could fetch you $200+ by itself. I guess my "issue" with this whole project is that (for the most part) all of the systems you are implementing are pretty much already available as emulators and most are done pretty well, clearly they aren't all 100% but I think you get the point, plus since you aren't planning on using cart slots or OEM controls you've already lost all of the "actual hardware" fan boys that refuse to use emulators based on principle alone, so this won't be any different.
All that being said, I personally would still be interested in purchasing one of these units even without N64 purely for the convience, but beg that you consider adding N64 later and perhaps Atari Jaguar too... basically any cart console would be amazing!
I do have a couple questions too. Will this system be compatible with usb hdd's as well as SD and... are there plans for a UI that would allow for cover art/game info to be shown for game selection? Similar to hyperspin and/or launchbox frontends, maybe not THAT customizable but I think you get what I'm talking about.
Keep up the amazing work you are doing, if this is as well done as Hi-Def Nes...it will be awesome!