The biggest risk is if all the most active communities end up centralized on a handful of the biggest instances like they seem to be right now, that means a bad actor would only have to buy up those instances to control almost all discussion on lemmy / kbin.
However, it would much easier for mods to migrate their community to an uncompromised instance than it would be to migrate to a new site completely. Jumping from reddit to lemmy / kbin, users have to abandon their old reddit accounts, move to a completely new website with a completely new interface, and start over from scratch. Jumping from one lemmy / kbin instance to another, users would just have to unsubscribe from the old community and resubscribe to the new one.