I personally don't think sgIII will get the multiwindow support from samsung but that is me and could be 110% wrong lol.
I hate the feature anyway.
I remember the HTC Eris went from sense 1.5 to sense 2.1.. skipping sense 1.6, 2.0 and more, so they will skip versions IF they are ready to go..
since we get leaks, which I suspect is Samsung doing free beta testing on us, hopefully we will get the latest. doubt it though
unlike our Devs, if they are working on updating their ROM and are about to release THEN a NEW base comes.. usually the Dev will port to the new base, Samsung will just release what they have and take forever to put out the new. that's my experience, take it with the smallest grain of salt..