The Jurati Borg, yes, definitely. The “old” Borg, definitely not — their story is done (or should be). Though you could maybe do more with their follow-on effects (say, the XBs) if anything more is done in the PIC era.
Now, for machine threats I would like to see more of, you’ve got the extragalactic cyber-Cthulhu things out there — that could work just as well in any later era, such as SFA’s.