A quick google suggests a plastic pitch is good for 8 years so Raith Rovers pitch will be that age when the ban comes in.
For me Falkirk should be allowed to keep their pitch until it needs it's 8 years old if promoted to the top tier.
Apparently the installation cost of a grass pitch of the required standard would be over a million quid and the yearly upkeep 750k mainly due to the price of electricity for the lighting rigs used to keep the pitch in tip top condition.