1. for low end? hard to manage? they're not saying they're going to make it 3D and add a ton of effects, they just want to make it easier to add game modes and game changing mechanics in itself, as the AU1 source code is quite outdated and "it's terrifying to add in more things because the game is so fragile." And I don't know what's that about it being hard to manage, going off with the first quote, the source code is too fragile to even add anything completely new to it, so there's no real moderation, as it was not implemented in the first place, and no way to add new stuff, as it's too complicated to do so, so the two things that do have to be maintained or "managed" are: bugfixes and servers, and neither of those pose a real problem.
2. "Among Us 1 servers will stay alive for as long as it has enough players to start games. [...] And even if Among Us 2 gets lots of players, we'll just run both at the same time. If Among Us 1 servers shut down, I will open source the code so players can run servers instead."