Maybe I skipped over it... but skimming, I saw no mention of support for Trackballs, Spinners, Steering Wheels, Pedals, Shifters, LCD 3d Glasses, ...Nor dual Time Crisis Recoil guns.
If thats so, then why bother? Many of the biggest name, and best classics, have analog controls...
Tempest, Arkanoid, Centipede, Out Run, Mad Planets, Supersprint, Race Drivin, Sinistar, Kick, Major Havok, Pole Position, Marble Madness, Star Trek, Star Wars, Daytona USA, Continental Circus 3D, Spy Hunter, Crystal Castles, TX-1, Paperboy, Return of the Jedi, Super Hangon, Afterburner II, Stun Runner, Rampart, Shuuz, Atari XO football, Discs of Tron, Enduro Racer, Golder Tee, Any Bowling games, any driving games, SanFranciso Rush, Tac Scan, Terminator 2, Thunderblade, Point Blanc, Time Crisis, Area 51, and over 1000 more.
Support for Mad Planets alone would be worth it. But having actual hardware output support for things like Force Feedback to an outrun shaker motor, 2 way gear shifter and lights for Spy Hunter, and 3d LCD glasses support for Continental Circus 3D (the effect is jaw dropping), would make me, and plenty of other pour out our bank accounts.
While money is always tight, we always find ways to get what we want. Especially if its things that we currently do not have in Mame... like actual Arcade shifter support, 3d support, easy hardware force feedback support..etc...
And even at $300, would be well worth the quality.
As for 32gb card storage, to me, thats not enough either. Maybe at least add one slot with 64gb microsd... and one input for an actual hard drive. Ability to run laserdiscs, and multiple emulators is a plus. (especially since sega master system also has 3d LCD games. I believe Famicon does too.. but probably not as good as Segas offerings). Mames set alone is way over that... and there was no mention of Jukebox support.. which also would be nice... as well as require more space. I suppose network cable could provide remote storage access.. but not everyone wants to configure that, nor has the cables running to the spot.
Also, is it mere Stereo output only? Because many games support more than 3 speakers. Games like TX-1 had speakers in front left and right, seat, and the rear. Gave true surround sound ability. Even Segas Turbo has 3 speakers... and thats way back in the 80s. Sound quality is important to me as well. Ive gotten very spoiled with a good set of headphones.. and have trouble dealing with horrible cheap onboard sound that is generally on generic motherboards. My Soundblaster Audigy, which is ages old... destroys many of the brand new generic sound chips out there... even besting my new Samsung Phones quality (sadly).
Finally, I think you should Nix composite out. You cant even find a tv that used it... and the quality it puts out is horrible. At minimum, svideo... But Id rather see Component support. HDMI is interesting, and may be needed once all the older component tvs die... but Id personally use Component out on my older tvs - which is closest to RGB, or if my Arcade monitors hold out... straight RGB. I, nor most people here, can stand Composite. Svideo quality is barely tolerated.
Edit: read some more...
Re the memory issue... Either add two 32gb sd card slots.. or maybe better... a usb port, in which you could plug in whatever you wanted. Such as a usb hub, card readers, or usb hard drives? Not sure if that would be a loophole or not?