Once you get your home or server IPs connected to black market forums, drugs, human trafficking or kiddie porn sites and your life (and your family's) has suddenly become more complicated, I wonder how many will still be eager to run Tor exit nodes? Maybe a few dreamers and anarchists.
Tor exits will be shut down one by one, either by the owners or by the police/state.
What we need to come up with is a fully encrypted, anonymous, self-contained super-internet of something like Tor "hidden services" only.