Linux-next is rebuilt every day based on Linus' current kernel. I merge
all the trees I have been told about and fixup minor conflicts (sometimes
reverting commits, sometimes applying patches). So everyday, linux-next
is completely new. I do not care if the trees I am merging get rebased.
I have only had a couple of occasions when the merge conflicts were so
bad that I had to drop a whole tree, but they were fixed up the next day.
Linux-next has only one downstream - Andrew's mm tree and he bases on a
particular day's linux-next tree each time he rebuilds mm. Testers just
need to take the complete tree (which isn't too bad if you are using git
since all the linux-next trees share a lot of objects).
Does that answer your question?