Q: Can some feats be "Swapped out" for feats that make them obsolete (perhaps with a caveat that the new feat "Swapped in" must be one that you could have qualified for at the time you took the feat being "Swapped out" (or else, equivalent mastery or less in that feat mastery category)? I was thinking, for instance of the armor feats that progressively make you 25%, then 50% then 100% immune to crits. Thus one could play the guy "getting better" without falling behind the guy that takes other feats (which don’t become obsolete) and who then gains the 100% immunity feat, and ends up "ahead" of the guy who took all three feats.

Feats cannot be "swapped out" at a later date. Feats that become obsolete were a deliberate design choice by Mike Mearls: they force you to choose between gaining an ability now, and losing out later, or doing without in the short term in order to be more powerful over the long term.

I am sure many GMs will house rule differently, though!