I'm pretty sure that was Notjohn's obligatory "I'm sticking with Sigil 0.8.x" sentiment, rather than a relevant commentary on the OP's primarily Sigil agnostic concerns about EPUB3 vs EPUB2 creation.
As you say though, Sigil has never really absolved anyone of not having to know a single thing about the structural requirements of how epubs are constructed. EPUB3 wil be no different in that regard. There will still be a learning curve for those who don't know the differences that EPUB3 brings to the table (just as there was a learning curve when they learned how to construct/validate EPUB2s).
So it's not really about "allowing the dust to settle," in my opinion. Its about deciding whether you're willing to learn anything new or not.
But like you, I believe the next version of Sigil will greatly lessen the hurdle to creating EPUB3s for the casual user. All without affecting those who prefer to stick with EPUB2. I honestly can't think of a single reason why an EPUB2 aficionado would hesitate to use Sigil v0.9.3 (other than for hardware or OS limitations). At this point, there's very little dust on 0.9.x's EPUB2 abilities in need of "settling." I would call hanging on to the 0.8.x series at this point (other than for the above mentioned reasons) self-deprivation rather than a strategy.