Technology and Magic research
Now I know basically anything will be able to be modded in but I think the original cannon should include...well, cannons and such. That is as magic research and spells should (and almost certanily will) reach the plateau that is hugely powerful so should the mundane tech tree.
If a game lasts a few hundred years, or longer, we should see muskets, cannons, etc is my basic point. I guess this would make the game sort of steam-punk-ish but the logic is there. And I for one can't wait for mods for a huge real and magic tech trees for loooong games.