As a Universal Orlando Employee that works with and around the ride (Our base of operations is right next to the building between BTTF and The BTTF store.) and having asked around. It is ONLY rumor at this point. It will be closing, but the feeling I've been getting is it will be for routine maintence and upgrades.
I think the simpsons idea is riduculous to replace a ride that holds true to the Universal name. It would be another jimmy neutron ride.
I have even asked the management and no real official or unofficial word yet. other than that it will be closing late Sept early October.
EDIT:: and as for the running half capacity, etc. that is only done as a cost saving measure. Seems to be the latest buzz at Universal is to save energy.