Besides sculpting, which is number 1 on my wish list, the possibility to load two TG documents at the same time. I know, you can load a second document into an older version of TG and I do that a lot, but it doesn't always work properly because some functions are missing in the older version and the nodes often become detached. This would be a real time saver, at least for me, because I often copy nodes from older iterations to the new one.
As far as sculpting is concerned: that' s already possible with the painted shader but it's so complicated that it doesn't pay off.