- 2d6 Skills: A unified skills system could easily use the 6-, 7-9, 10+ roll system from AW. This way, a small bonus has a large impact and it provides some narrative elements as the GM can use the at a cost of 7-9 to their advantage
- Playbooks: The real gem is playbooks as you can actually play an entire game of Apocalypse World with just your character sheet. Having a two page rules/character sheet for an OSR game contain everything needed for play would be extremely useful, especially for the groups where no one wants to read the rules.
- Codified GM Rules: While not as old school in feel, having a few set actions to help a GM could be useful, although I personally would not include this in a game I write.
If I have time once I finish all outstanding projects, a PbtA spin on AD&D would make a nice project so I can finally have something I can play without my players dragging their feet and procrastinating before they actually read the rule book, and that I can enjoy.