The only down side I can think of is if the decision is made to make successful takeover's dependent on widespread use of all these extra options. Just as takeovers can be immensely boring with nothing to do right now, it would be annoying if takeover's instead became a chore with so many nobles having to organise synchronised action for success.
This is something I was thinking about, too, but couldn't think of a good way to say it.
I guess I'd be concerned that we could go too far with it, and TOs could only be successful if you had a lot of nobles clicking their "Be hostile" links every turn.
