There is "blazingly fast" where you also have to only include SSDs, still see your root drive taking seconds to populate data for, and still requiring admin for the whole app with those ugly underlines otherwise..

And then there is literally instant, for literally everything, while the app itself is in normal mode and thus preserves the non-admin benefits.

a) Not for the app, only for Everything

b) Those other file systems could also be indexed by Everything (though via a slower mechanism). Also given the primacy of NTFS, I'd definitely trade the ability to have folder sizes for drives I rarely use for the instant calculations on drives I use all the time

c) Good. Waiting for MS docs could mean a few more decades of wasted potential