I also agree with CON being the polymorphers governing stat as opposed to STR. Though I'm definitely concerned about how the STR will fare in D:OS2 if Man-at-Arms remains the sole skill tree governed by it.
I suggest that Polymorpher is made as something of an enhancer skill tree meaning that some skills can be used to the benefit any character and others for more focused benefits/enhancements to the specific types of characters.
I think that this would benefit simply because the way it's looking now, neither a STR or a DEX based skill tree is coming out of the vote and this would be a decent way to help these two out and not make a mage type character the go to. Since they're pushing the competitive multiplayer as much as they are, this could be an important thing in terms of balance for the game.