Hm, this doesn't seem like the greatest thing, because already going "human" is basically the same as going "watcher" in most cases, so it doesn't add much (ie, anyone who goes human, we can usually assume is watching).
In addition, it sounds like with this idea, someone could go "watcher" and then still build... which I am sure the trolls and hackers would LOVE. they would like it much more than how it is now.
What would be cool is if selecting watcher disabled your ability to build. If you literally added a new race to the game that has no buildings. I am not sure if there are any war2 programmers that are capable of and interested in making these kinds of game adjustments though.