Save selected as.. would be a very powerful feature. Especially for splitting up 4GB-6GB .psz scenes if you have multiple chunks.
At the moment you have to delete a selection of chunks to trim down file, then save. Then load back up again to split the other half, which can take a long time as large GB files can take over 10 minutes to load sometimes, especially across a network (even on the local drive)
Being able to multiple select the chunks you want, then do "Save selected as.." would be a real head ache saver!