To add to this, I've noticed that the !expert bang will load up the last-used assistant config now, with the new assistant UI. It would be nice if it went directly to some standard "best/expert" model (gpt4o? Claude Opus?) with internet access enabled, to better match its previous behavior.
!code still seems to work the same as ever. Those are the two modes I typically use, so this means using !expert actually takes me to the code assistant in practice.