Ok, we should get some things straight on this possibility.
Having only 13th century equipment does NOT limit cultural diversity. This change implies we would still have 13th century equipment of asian, middle eastern, european, origins (as well as African, or whatever else). In this way, themed characters would still be perfectly viable.
There are a LOT more 13th century weapons and armor that are not in the current mod that could be added. So removing 14th-16th century items does not necessarily mean there will be less equipment diversity either.
I think this would be a cool idea, if new items were added to replace the old.
I don't think crpg (and mount and blade in general) are fun because of the diversity. I think it's fun because it is one of the most realistic and intuitive (in terms of combat control) multiplayer fighting games in existence. Limiting the items a bit more for the time period, while maintaining diversity, would make it more immersive/fun for me.