Hello Faré,
Yes the prologue and epilogue is (or will be, in the publicly and officially sanctioned ASDF-way once I send you my small MKCL mods for ASDF 3) used after all. Maybe not really by ECL, although it should, but by MKCL. It is an essential part of the program-op processing.
You are right about the fact that prologue and epilogue are not very well designed as they stand in ECL (and how MKCL inherited them from ECL). But they really make sense if they are considered in the context of #'compiler:build-program. I would even say that they are essential in the context of #'compiler:build-program.
I am currently putting the finishing touch to ASDF 3.0.3 on MKCL 1.1.7 on Windows (3 more tests to fix). I should be done somewhat shortly and after that I'll sent the ASDF list what I have got, merged with ASDF head.
Sorry if I could not reply to your ecls-list messages more promptly but I was out all day participating in a double fencing tournament. I did basically a somewhat marathon-like 8 hours straight of competitive épée, so I hope you will understand if I stand a bit out of phase with my computer keyboard for a few more hours while I try to recover.
Cheers,
Jean-Claude Beaudoin