I forgot to mention one thing. Have you ever tried to line up casing
with the edge of a door frame? About ten or fifteen years ago I did
exactly what you intend to do (not with MDF though). If I wasn't
embarrassed about how it looked I'd run over and take a picture for
you. This is one of those seemed like a good idea at the time type of
things.

The reveal is there for a very functional reason. Lining up along the
whole edge is difficult. Not impossible, just a pain in the ass. The
tiniest discrepancy shows up. So you're either left with a lot of
sanding and/or filling, or a little bump in what is intended to be one
smooth surface.

R