Spiner himself explained,

One of the ideas that John Logan and I had about what the next film would have been was a Justice League of Star Trek. Something would bring all the great Star Trek villains together, from Khan to Shinzon, and Picard is the only person who could stop them and he actually has to go through time and pluck out the people he needs to help him. He goes back to the moment before Data blows up and takes him back to get Kirk and Spock, and go even further back and get Scott Bakula’s character, Archer.

I can’t imagine it would have been good, but boy do I wish I existed in a universe where this movie had been made.