Check out all the rules around how MLS and MLS Next aquire players.so that effectively circumvents the MLS territorial rule?

Roster Rules and Regulations | MLSsoccer.com
Official MLS roster rules and regulations

Once you're under contract with a particular club which I'd assume they'd try to do to any potential talent in their area. The club basically owns you and a formal process needs to occur if you're transferring to a different club.
MLS Next knows who the top players are by 16 so it would be difficult to just move and play for a different club if you've already been identified.