This does not even have to happen in 30 states, just start with California. The amount of $$ and time that Democratic candidates would have to spend here to keep their margin would totally change the contours of the race.
Someone tried to start an initiative drive here, and I wrote about it to the GOP national HQ, but they did not even answer my email. Without any funding, the drive went nowhere.
With everyone fleeing California at some point Congressional seats will be lost as will its electoral affected.