Anomalous wrote:As for unlocking – once unlocked, stays unlocked for the rest of the current game, but could become unavailable again…? And once some percentage (at most 50%) of your team has unlocked some upgrade, it could become available to all on your team.
Hello Great Library of Alexandria. 
If we go for personal trees, I'd like that a lot in public games. Not sure if this renders the trees obsolete in a coordinated team.