I never said we wouldn't do VST3. We adopt technology when it makes sense to do so and actually benefits our application and larger user base. Until literally this year there were no plugins exclusively in VST3 format that made it worth the significant development resources to invest in. And there was nothing that we needed VST3 for to implement it. The prochannel is all VST2 extensions for example.
What made it worthwhile for us to do finally in X3 were 2 factors:
1. The ARA implementation was more natural to do based off VST3. Although Celemony had a VST2 implementation their VST3 layer was better tested and I didn't want to do a huge new implementation based off an older standard. Also I was refactoring large areas of our VST engine for this and it was a good time to make such a change.
2. A few big plugin vendors such as Waves have stopped maintaining their VST2 releases (due to resource constraints not due to limitations of VST2)
My original perceptions about VST3 are still valid after having developed this. While its a more modern API there is virtually nothing that couldn't be achieved by some simple extensions to VST2. I don't fault Steinberg for wanting cleaner API (most developers are hate old designs) but it could have been handled in a more transparent and backwards compatible way than they did it. VST3's object model seems over-engineered to me. I didn't have much trouble getting it but I think many developers will have a hard time with the excessive abstraction in the API's. This and the completely lack of backwards compatibility are the main reasons for its slow adoption. One good thing in VST3 is that the basics like sidechaining are part of the spec so there is slightly less creative interpretation among vendors.
Anyway we have it now and a good side effect of doing it was that I cleaned up a lot of the VST2 and general plugin code as well so it benefits all users. I have written a blog post on X3 VST enhancements that will come out soon.