I personally think the Sentinels was left with far to many unknown factors. I mean would the army that attacked in DoFT stand a chance against Phoenix? I doubt it, how do you adapt yourself out of a telekinetic assault that tears you apart on a atomic level? The sentinels adapted by taking form or shape of objects attacking them directly (like Fire) or things they made contact too (the rock they touched), something like energy that Bishop employed they didn't show any signs of developing resistance against. They overwhelmed and overloaded him, with that in mind, I don't think they can adapt out of Phoenix, Quicksilver, Storm or (if they should change to metal) Magneto. But again this is just my opinion based on what the sentinels showed on screen.