Does anyone know:
Lossless 'should' convert to lossless. I am not sure about this with Traktor, though.
Stacking the stems don't lead to exactly the same master track.
Vocals stem will contain everything the algorithm deems vocals; sometimes it contains snippets of vocal like elements, especially when converting non-vocal tracks.
Only NI knows if there will be an update of the tool, nobody else.
The best answer to all your questions except the last will be to try it yourself. You can download the installer without a license and start it in demo mode for 30min. That should be enough to convert a couple of tracks, exit to save the collection and then restart to test.
