Attract more will only select one of the original 30 and will skip over any new games.
As of maybe 2 versions ago a "uninstall" option has been implemented. It removes all traces of Hakchi and re-flashes the original kernel.
In the week that it's been out there have been zero reported bricks.
Thanks so much for your answers. I might hold off on hacking mine for a while to see if people keep being happy with their hacked systems, and perhaps to see if the attract mode feature can be updated yet somehow, but the latter two answers you provided do make me feel more or less safe enough to give it a go at some point.
To be clear, I'll never need 80+ games on there necessarily, just 20 or so more to fill in the most pressing gaps for me (Tetris, Faxanadu, TMNT 2 and 3, Bionic Commando, Crystalis, StarTropics II, a few more Mega Mans, Mighty Final Fight, Power Blade 1 + 2, Ice Hockey - which I still can't believe Nintendo skipped by the way - and maybe a handful more...).
Yeah, unfortunately Mario will just skip those games. Which is a bummer because I love that feature, too! I just leave it on when I go to bed sometimes, it's very relaxing

Maybe the creator of the software will work something out? I could be wrong, but I think some of the games seem to have specific demo routines, while others just run the game for a while.
Ah, I had a feeling he might. That's too bad.
Just like you, I also put the attract mode on to have some fun and relaxing background visuals and noises! I always like attract modes and demo's in games in general for that kind of use. (As a sidenote: a game like SFV not having any attract mode was kind of a bummer for me, though I might be almost alone in that complaint.) Hopefully the software can be updated to feature every game as that would rock. (Then again, if nobody else besides people like us is asking for it, maybe the chances are low...)
I'm guessing Nintendo is going to remove the USB for any future releases.
Yep, that's my fear as well, which would suck as that would probably mean no Secret of Mana, FFVI and Turtles in Time on my device in the future (unless Nintendo adds them, which I doubt). Or, if they want to be particularly protective, they might even reconsider doing any follow-ups like a Snes Classic completely (unless the success of the Nes Classic and its profits are being the bigger draw still).