For my part, I'd like to ask him:
- Some things on Magnamund, from a world-building perspective. The typical world-building questions, whether he started with a map of the continents or started by developing a smaller area (say, Sommerlund) and expanded the world as it needed done.
- Which version of (A)D&D he created it for (I think he may've said 1E in a previous interview, but I'm not sure).
- Whether the original feel of Magnamund in his gaming was like what we know as Lone Wolf, or whether it was more typical D&D.
- What the monsters were like originally; IE, did he work up new stats for a Giak, or simply use a goblin? Were Vordaks skeletons with psionic powers? Helghasts simply doppelgangers with a modified shocking grasp?
Probably other things, but that's all I can think of ATM.