I don't really understand the mentality towards platform stability, either from PH, or from users here. The stability of the software isn't going to be affected by this implementation, there is of course the possibility that a plugin - or a combination of plugins - might cause an issue, as is the case with any VST compatible platform, but you don't have to use VST plugins if you're concerned it will affect stability. Without them it will behave as well as it did before.
I've been fortunate enough to have had access to the beta for a week now and have been using the combinator to build complex synths using VST instruments and effects, I've also tested stuff like halion, kontact, omnisphere, amplitube and a whole load of different VST synths and I can report zero issues so far, it is a logging version of the software so it is a little sluggish sometimes, but it is behaving in the same way as previous logging betas have.
I can't guarantee I won't post this and then suddenly have a load of crashes, but I'ts done around 18-20 hours testing without issue so I'd be happy to say stability isn't too much of an issue so far and for those that aren't convinced I'll repeat, YOU DON'T HAVE TO USE VST PLUGINS!