It would be extremely shortsighted to prevent 100% inter-operation of HSR and Caltrain bullets.The notion of 90 mph service comes from Caltrain's existing electrification plans, which are about to be made obsolete by HSR. To play better with HSR they are going to have to increase their baby bullet speeds a bit.Also, there is no such thing as an upgrade to catenaries from 90 mph to 125 mph.