I know some people won't like this, but I think it's a good idea.
A Halo: Reach forge-mode option thingy that you can only use inside houses you own (free or bought). It would pause the game if that would be a problem. Also, it would be nice to have some sort of icon next to containers that do NOT respawn their contents. I lost my Fin-Gleam in Oblivion that way. Even when someone says "Oh X container in Y room in the Z corner is a non-respawning container, I am always a little edgy...
Nothing freaks me out more than the moving mannequins at my Honeyside house. They don't just reposition themselves, they actually come off their bases as if they walked.
Really? That sound cool! Maybe the could make some sort of enchanted mannequins that you can equip with stuff and use as (a) training partner(s)... Don't say make a mod for it. I'd liek my previous two suggestions to be something official so console players don't get ripped-off. If they make it of course....