At long last, sculpt masking is in trunk!
Big thanks to everyone who helped out with uploading test builds and providing feedback on features and bugs. Thanks in particular to Brecht for doing code review, and to the Blender Development Fund for sponsoring the work.
Documentation is on the wiki. We’re getting pretty close now to feature-parity with SharpConstruct ;)
Edit: With masking safely in trunk, I’ve removed the masking branch from github and merged the updates to the skin-modifier branch. If you have previously saved files using the skin-modifier branch, the skin data (i.e. vertex size and root markings) will be lost. This is due to the skin data and paint mask data sharing a CustomData layer identifier until now.