Hi Tim -
VisualWorks (and probably other VMs at a guess) got some serious benefits out of polymorphic inline caches. I rather doubt inline caching is going to work in an interpreter but there might be some advantage in making the current global cache polymorphic. It could be a decent experiment to try out as a class exercise for example, since even if it turns out not to be beneficial it would be instructive and require all the usual investigative, analytical and explicative skills. I'd even volunteer to help with reviewing and grading, subject to time constraints.
But isn't the global method cache polymorphic by definition? It maps class+selector -> method (actual class of object; not class where the method is defined in) and unless I got the meaning of the word wrong this is polymorphic, is it not? ;-)
Cheers, - Andreas