What about simply changing the number of witness votes per user to 5?

So simple and more often than not, the simplest solutions are the best. The only question is then what happens to the users votes that have already gone to more than 5 witnesses.

And regarding the DAO, those funds should be burned ASAP and it should be dissolved.

I've been reliably informed that the money already sitting in the DAO is protected but I don't see any point in that much SBD inaccessible to anybody and just crying out for a hacker to have a go.