With our central processor units we developed a process model where each process was isolated memory wise from each other. And then went on to destroy that model with threads... but I digress. This process isolation culture was probably born from shared systems where each user needs to be isolated from each other. but has served us well with in providing robust single user systems. and has proved critical with the move back to shared cloud computing.
Graphical processing units hove no concept of memory isolation. and have no culture of wanting it. They were high performance units for a single user only. At this point trying to introduce isolation levels would probably be a lost cause. Many people would be very unhappy at the performance hit that would be required.
But yeah a GPU in a shared environment spooks me as well.