Now that I've realized I went overboard planning a "simpler" version of my Treasures, Serpents, and Ruins house rules (that made things more complex due to additional cruft accumulating), I've decided to more or less stick with what I have. There are one dragonborn PC (oh, and one retainer) and one changeling PC still active in West Marches, and going forward I think I won't allow any new PCs of those races. NPCs may still appear, but I think I will weed them out over time. I'm also thinking I don't really need the half-elf. Play and elf and fluff it as a half-elf if you like. I'll keep half-orcs because I have a fondness for them. And gnomes may be retained, or just folded into the dwarf or halfling races (Willow style halfling magic-users may appear instead of gnome illusionists).
So simplify the races allowed, and keep the current line-up of classes.
Next, I'm still considering the idea of Chainmail Arena, but also a simpler version of TSR house rules. Today, I'm considering merging the two ideas. Make a simple BX style set of classes, and use Chainmail combat. Part of me wants to, similar to the Dungeon! board game, use 2d6 rolls for all attacks like the man-to-man and fantasy tables do. Part of me still wants to retain the standard Chainmail mass combat dice pool rolls, only on a 1-1 figure scale instead of 1-20. I think for actions involving higher level PCs, or groups with lots of men-at-arms/retainers, versus large groups of humanoids or pack monsters (wolves, stirges, etc.) the mass combat resolution system will be fine, and faster. Against "heroic" enemies or more dangerous monsters, it would make more sense to play out each round of attack/counter attack, I think.
But will it make the game more messy? Probably. And will there be arguments about when mass combat rolls or man-to-man/fantasy rolls are appropriate? Again, probably.
Also, I need to consider how to stat up monsters, especially those that don't wear armor. And do I want to keep the weapon vs armor tables for man-to-man, or like the Dungeon! game, just give each monster a target number for each class to beat?
If I go with the target number by class, it would be easy, because every few levels will just add +1 to all rolls for that class to simulate greater fighting power. But then it eliminates weapon choice.
And then, what about monster attacks on PCs? Will PC target numbers depend on armor worn? Or class/level? Or a combination? And what about rolling on the fantasy table?
Hmm, need to consider this more carefully, I guess. And take another look at that Grey Elf PDF compilation of how to run D&D with Chainmail combat to see how others did it.
I'm going to post this even though it's a half-formed idea, so I'll be able to reference it easily in the future. And some of you may have a few good ideas to add in the comments, too!