I'm sure many folks would agree that this could be a useful facility, especially for writing "version-independent" scripts, or at least to know whether you need a "require 5.00X" (and what "X" should be) in a script that has a version dependency.

The difficulty is that this is an open-ended problem. It's not clear to me that the set of "features" to be indexed could really be enumerated coherently. This is the kind of problem that might best be tackled by a search-engine approach: you index all the "perldelta" pages according to word occurrences, and search it "google-style": enter a few keywords or a phrase, and get back a list of locations where you'll find relevant text.

(You'd need to actually read the cited text to see if it's a reference to a feature being introduced, or one being fixed in some significant way, or one being deprecated...)

(update: fixed grammar)