^
The problem with adding GlaDOS or anything concerning the Portal is that it could fit anywhere within the large continuity that is between Half-Life and Half-Life 2. I would prefer that ValVe save more revealings of GlaDOS for Portal 2, unless of course that turns out to be a prequel game to Portal as suspected.
Getting “more down to Earth” in Half-Life 3 would definitely be going against the current of where the series is going, to me all evidence is pointing towards an even more epic entry into the continuity what with the Vortigaunts hinting at Gordon’s larger destiny. Then there’s G-Man now without control of Gordon, will perhaps resort to renegging on the restrictions of his powers/abilities in order to ensure that things happen as he wants them to.
Basically, I just don’t see it being a down to Earth story.