So now the ruleset idea is maturing, and I've entered a new module into the rpg project of the repository, for Drudge (rpg_drudge.module in the rpg/rulesets folder).
Workflow: lower-order object types will be part of a basic system, possibly Drudge or possibly something lower than that. You may 'import' a ruleset of objects & game rules from such a module, which uses hook_rpg_ruleset. The module will have an array of types, and functions that define those types.
When importing the ruleset, you'll see a list of types defined by the module, some of which might require types from another module (in which case they'll be grayed out if those parent types don't yet exist). You can select them all, or just the ones you want, and they'll then be loaded into the database and cached, and be available to override as any other type.
As with cck & views, you'll also be able to import/export types as php scripts, which could be shared/contributed or used to create new ruleset modules.
Ok, back to working on it now. There are notes scattered through the project for anyone interested in digging into that.
Aaron