I would take everything to do with a third film with a grain of salt right now, considering a third film hasn't been officially greenlit yet. Spitballing is spitballing. I'd put more credence in the Klingon side of things. That being said, the Borg got screwed up so thoroughly by the PTB's last time I doubt that would be a very good idea. They're probably left far far away. Just like they never fit into DS9, they wouldn't fit into TOS either.
'If the Apocalypse starts, beep me!' - Buffy Summers
'The sky's the limit.....' Jean-Luc Picard, 'All Good Things'
courtesy of Saquist