I'm reminded of the dodge that religious institutions have achieved. In exchange for tax-exempt status, they are forbidden from explicit political stances and endorsements; yet in practice, many churches are highly influential in the political process, as they of course are allowed to take moral stances (abortion being the big one), and encouraging their congregations to "vote their consciences", etc.

Seems to me that Twitter advertisements would likely take the same path, where the bought political influence is instead abstracted away into generalized "awareness campaigns", push-polls, etc.