But you're okay with spending the extra money per game?
Its not gunna happen. I don't know what Portal 2 mods look like, but I know that TES mods are extremely deep and often end up relying on changes to the game itself (see: Oblivion Script Extender). That's impossible to do on a console version, as it needs to use an edited launcher of sorts.
Besides, if I recall correctly, Valve us using some sort of Steam application through the consoles, which will probably allow them to host their player-made mods in a way that they don't have to pay Microsoft or Sony their silly fees for DLC. Bethesda doesn't have that. They'd have to ask Microsoft to hose them, which would make them.. not free.