Unlike the naysaying commentators on Trekmovie, i'd welcome more guest spots from TNG-era actors/characters, so long as it makes sense and fits into the show narrative. The Doctor is quite likely, the most experienced on the Borg (outside the obvious former Borg like Jean-Luc or Seven). If he appears as Dr Zimmerman, it would also fit with the possibility of "Hologram Data", or maybe even as a developer of the 24th Century "Mobile Emitter".
Robert Picardo... Make it so!!!