The Feature Macros proposal is only adding macros and vars to Clojure---the reader isn't modified at all. Since all of the things you mentioned are reader macros (as you pointed out), Feature Macros never even see them, so they won't be affected in any way. (Reader macros are expanded before regular macros are, so regular macros don't see things like `#(...)`, they see `(fn [] ...)`.)
The great point made in the README is that we can't generate feature expressions. With feature macros we can have macros that generate cross-platform code. That's big in my mind.
That hasn't been a problem with reader macros in the past since you don't need to generate `#(...)` if you have `(fn [] ...)`.
I don't understand when I would ever want to generate a feature expression. The goal is to generate platform-specialized code. You never have to generate code that generates platform-specialized code!
