Before we get into the controversial subject of magic I think it’s time to look at the core mechanic that would lay at the heart of my version of D&D.
I want things – as much as possible – to be resolved with a single roll.
I think D&D is, at heart, an heroic game so I want a flat probability and meaningful crits and botches. So a single die is the way to go with a 1 being an automatic failure and a 20 being an automatic success (of at least minimum level, of 1).
Even combat (and damage) is something I’d like to see done in this single-roll way, especially as this abruptly makes a sort of sense of ‘Armour Class’ which has always been a sticking point for me. Resolving avoidance and resistance to damage in one helps deal with the issues I have with it at the moment.
Using roll differentials to determine damage means you can retain ‘glancing blows’ where multiple dice and damage bonuses would normally create a lower limit.
More detail on this when I get to it, but the basic system would remain d20+bonuses Vs Target number.