Based on a brief 20 minute play, my experience is now generally positive v9.2.1 (build 542) is largely positive ((edit: spoke too soon - see further updates below)).
Masking seems to work reliably (in that it functions) and looking at some of the concerns above: I can export and I do still see Fine Contrast controls (and they work) based on a FP7 license.
Bits of note:
Performance continues to be slower than I would like, especially when the number of masks increases.
Sky Masking via AI is poor (I’ll use the Control Line workaround for now, but this does need improvement). Look at all these trees it thinks are sky!
Update: Performance really tanks with usage.
I’ve a folder of 69 unedited photos. I’ve just gotten as far as editing 4 out of that number, and exporting it. Everything is sluggish as hell, and exporting just that final image (not even the other 3) took 1 minute 11 seconds. 1 AI (people) mask, 1 graduated filter mask, 1 auto-brush mask. It was even black and white.
By contrast, loading PL9 and editing one single image felt much snappier, it had multiple AI masks (8+) plus other masks, and exporting it took 15 seconds (colour).
As I write this, I haven’t touched PL9.2.1 (it’s not exporting or anything) and it’s using 12% CPU and a whopping 70% memory.
The performance/optimisation is awful.
Restarting PL releases over half of the memory in usage and CPU use drops to minimal levels.
Update 2: Having edited just two more photos in the same batch, and exporting each individually, I’ve just hit a record high export time of 2 minutes and 38 seconds for a single image.
Update 3:
Further experimentation indicates that export time more than doubles after the first export, even after a fresh restart.
Nothing unusual is occurring with these images - in many cases there are only two masks being applied - no other big changes explain this performance shift (they’re from the same camera, shot on the same day, same shooting and editing processes being applied…)
What the hell did DxO do?! 
Update 4:
Downgraded to 9.2.0 and ran more tests with the same batch of images, same editing process etc. etc… and performance is right back where it ought to be (which is still slower than PL8 but…!)