Pre-carbon fiber and pre-microprocessor Borg. They'll drag heavy machine parts behind them, and move even slower. Still faster than the Gornn though.
I was thinking I wouldn't mind seeing Curzon Dax, he's already tied into the whole Klingon story, but Memory Alpha tells me Curzon and Dax weren't joined till 2286 (same year as "The Voyage Home"... I love Memory Alpha). That's a continuity error I wouldn't mind hand-waving away, but I suspect it would bother most. I guess Aubrid, or maybe Emony, was the host at the time? They wouldn't connect to these story elements as obviously. Maybe I'll just go back to hoping for a Dax cameo in the Kelvin timeline...
Agreed, there doesn't seem to be any information on when Dax passed from Emony to Audrid. Emony is likely through the 2240s (as she appears to have encountered a teenage Leonard McCoy), and Audrid Dax was head of the Symbiosis Commission by the 2260s (her involvement in a Starfleet science expedition led by Pike during that period however is from the DSN novels and therefore non-canon).