My vague impression is that the VST3 spec is a lot harder to write for, which may be exacerbated by the hard design problems something like Rack for DAWs poses (it’s more likely to push into dark corners than most plugins would).
JUCE has abstracted a lot of this out, which I suspect has helped with VST3 adoptation tremendously, but I highly doubt that Rack for DAWs is using (or maybe even could use) JUCE.
I don’t envy Andrew’s position at the moment. He’s a better-is-better programmer dealing with the one of the premier worse-is-better-but-also-worse SDKs (and some increasingly wild speculation and personal animus to boot). My best guess is that V2 is in good shape but he’s hitting issues with Rack for DAWs and doesn’t want to handle a lot of entitled Redditors going nuts if V2 comes out without Rack for DAWs.