I could improve the starting equipment, and have a few quest items be cubable with particular items that you start with, thereby granting a random low-level unique or something to that effect.

Normal play should simply be fun. If it's easy in Normal, that's fine by me. As soon as Nightmare hits, things ought to become much more difficult, and by Hell... it ought to be Hell.

I've been considering making no enemies but a select few have complete immunity to X, but also raising their resistance. I think the point of complete immunity lies around 140, so raising that would make lowering their resists more plausible/fun with the increased implementation of items and skills that lower enemy resistances. They would still be immune for all intents and purposes for much of the time, but with enough skills or equipment, they wouldn't be completely immune except in a few cases.

But who knows.