Amazon's overall goal is to take a cut of pretty much every piece of economic activity. Taking a cut off of every payment made on the internet outside of their own stores is an objective greatly aided by a stripe acquisition
I guess that if Amazon threw a crazy enough amount of money at them, then sure, everyone has a price, but how is joining Bezos' empire helping them? There's very little synergy in the other direction, so the premium for such an acquisition would have to be very large.
When you put the premium there, along with how being acquired by Amazon makes the competition more attractive, makes me think that something like that is unlikely.