I've always considered it a retronym, purporting to be the converse of "retroactive." Prescriptivist that I am, I won't use it myself and I wince whenever I hear it. It's a bit like the devising of "analog watch" that only came into being after the emergence of digital timepieces, though by now that one has become an acceptable distinction.

At least it's appropriate to differentiate analog from digital in this context. Is "pro-" really the inverse of "retro-", or have they mixed languages here? Should we agitate for "ante-" instead?