Amazon kindle fire OS is modified from Android Gingerbread, which is a outdated Android version. If they want the OS more capable and more multifunctional, they need to work from a more advanced Android version or other OS. webOS in this premise is a good candidate, which can also help them differentiate from other predominant OS. And with ACL they could make Android apps portable to webOS so make their amazonapp store exploitable.
I would say DELL would be a better chance than Amazon. If DELL wanted to bet the farm on a Hail Mary long shot, buying webOS and pumping it onto products might be an option. A bad option, but an option all the same.
That said, in no way do I think DELL will purchase webOS, it's just slightly more likely than Amazon.
Amazon will not buy webOS. They have already designed the user interface they want and it runs on top of Android.
I think Amazon is the last possible buyer because they have the motivation and probably the only one amongthe alleged buyers with the ability to pull off all these works.