Star Trek 4: 8 Villains We Might See
2. Q
The last three films have focused on an individual as their villain, rather than an entire species, so if the creative team follow that pattern there's no one better than John de Lancie's mysterious Q. Bringing him back to the fold, and keeping de Lancie in the role, would mess with the rebooted timeline. Mind-bending blockbusters like Inception and Doctor Strange prove audiences have an appetite for getting their brains fried by a film.
Q presents an intellectual and philosophical threat to a team who are in need of being pushed to their limits, and we haven't had a Star Trek that tackles philosophy and theology since the awful fifth film, "The Final Frontier". Not that tackling such topics would be a boring change of pace- the filmmakers need only look to intelligent science fiction films like Interstellar or Arrival to see how films with bold ideas do well with critics and audiences alike.
Plus, Q is just a brilliant character. Irritating and mischievous, he could very easily bring out the humour in every situation, however perilous or emotional draining for the Enterprise crew. Having Q butt heads with Bones is to exciting an opportunity to miss! For a very different kind of Star Trek film, Q is the villain to pick!
If the filmmakers insist on recasting the role of Q, the best replacements would be James Woods, James Spader or even Toby Jones.