2437922:Aswell to prevent abusive mechanics such as shadowmeld/Darnassus, elusive untargetables and Kazamon, you can say that an ally that has captured the flag loses and cant have powers while holding the flag.
Not only would this remove a lot of abuses, it mirrors the MMO fairly well, considering you can't stealth or mount, and that after a certain amount of time holding the flag, damage dealt to you gets increasingly multiplied.