Another note is this: How can we get a VST/Audiounits/whatever kind of framework going that can be used in the various host system out there? I'm dying to have interoperability in this department!
you might be interested in the genesis of LV2, nee LADSPA v2. there's nothing stopping it from running on many platforms besides developer motivation; in contrast, you will likely never see AudioUnits on Windows or linux, and VST will always be a 2nd class citizen on OSX and 4th, 5th, or beyond on linux..
one of the goals, in addition to potential cross-platformability, is increasing the flexibility of the type/ports system to the point of 'PD external without PD'. i find it pretty exciting..