(Speculation)
I would say prolly not... Unless the demand and developers required them to.
As of now (afaik) Steinberg is the only ones supporting vst3.
Until others get on board, I doubt REAPER will.
And we also are excited about helping define a new, open plug-in API. Much of what Angus has written makes a lot of sense to us.
The biggest thing, though, I get excited about, is having a plug-in API that is compatible with open source licenses. The fact that VST effectively prevents LGPL or even BSD licensed plug-ins is completely ridiculous...