I've already answered the Launcher update here: Check for Launcher update!
Regarding the mask feature, the user guide should be clear about it: Clipping - Spine User Guide
Clipping is implemented CPU-side in all runtimes, as most engines do not support direct stencil buffer access or masking. Clipping can be a very expensive operation, especially if you use dense mesh attachments. Always check the performance of your clipped animations on your target platforms.
Most engines wouldn't be able to support it at all, unfortunately. I agree it would be very nice, but considering also how expensive it is at runtime, maybe finding an alternative solution would be better.
@gruen if you want, you can write an example of what you would like to achieve and I can help to find an alternate way of doing it.