Yes, the IPA is bound to future owners of the patents. (It would be trivial to get around if it wasn't).
And to clarify: the goal of the IPA isn't to make Twitter or any one company some blessed repository of patents. The goal is for many companies to adopt the IPA as a promise between them and their engineers.
How does that actually become legally binding? If the patents are assigned to Twitter, and are later transferred to an entity that never agreed to the IPA, what actually happens? I honestly have no idea how it would work out.
And I fully agree about the IPA's goal, I'm protesting against people saying that it should be treated as a benevolent patent pool now. On the whole, I think the entire patent bullshit is moronic and should be annihilated at first opportunity, but that's a different story.
Check out section 4. If the assignee attempts to assert the patent improperly, the inventor has the right to give out licenses. The inventor's rights are permanent, not a function of who happens to own the patent.
And to clarify: the goal of the IPA isn't to make Twitter or any one company some blessed repository of patents. The goal is for many companies to adopt the IPA as a promise between them and their engineers.