Things I wish D&D bothered to address – and which I would be tempted to pay for*
- Combat where a party of 4-6 adventurers have their gang of 4-6 retainers each, without it becoming a big glob of rolling 25d20 and blowing your brains out with boredom. Like small squad tactics or something, where your squad could be, like, a Hero, a displacer beast, and two Gnomes.
- Some sort of guidance on social encounters. (I know, I know! I’m a communist who likes social mechanics.)
- Advice on staging urban adventures – preferably as clear and as helpful as the dungeon creation and wilderness creation advice in Moldvay and Cook/Marsh.
- Some kind of rules or help on the Endgame stuff, so that it’s more than just, “Oh, I see your castle would cost $X bazillion gold, and here are your YdZ first-level Red Shirts, use them in good health.” The Mentzer Companion Rules are a step in the right direction but don’t really cut it in terms of practical advice.
- A Thief class that actually makes freakin’ sense in the context of the default skill system of your campaign. (Even the earliest editions of D&D had a skill system – yours.)
* = “tempted” is probably the key word here.