Stacked panoramas are now fully supported, but bear in mind that they use a lot of memory. You may have to use --build_pyramids=no and --build_raw_pyramids=no to squash memory use. The stacks are exposure-fused before they are stitched together, and each stack is processed as such and used for the final result, rather than using heuristics to make the stack assignments during the stitch and excluding redundant images from the result.
The full masking support refers to still images (when the viewer is at rest) and stitches to image file output, while the 'fast' view (while zooming, panning etc) will only show the 'stack parents' to save time.
Correct lens/source image cropping now makes it possible to properly display and render 'dual fisheye' images.
I'd like to point you to one interesting new feature, called 'hdr_spread'. With this parameter, you can select by how much the dynamic range of an exposure fusion is actually compressed. A 'classic' exposure fusion will compress the dynamic range to the same range as the input images, and this is what you get with the default, which sets hdr_spread to zero. Now with increasing hdr_spread, the dynamic range will be compressed ever less, until, finally, you arrive at the maximum value of one, which produces 'proper' HDR output (you'll need openEXR output to capture that). The HDR output from this process is actually generated with lux' modified Burt&Adelson image splining algorithm, so it uses a multi-scale approach and produces pleasing results. So if you'd like to produce an HDR image from a PTO holding an exposure bracket, try the new feature, it's as easy as
hdr_spread will also affect the fusion of stacks. Enjoy!