I don't agree - most mods are simply changes to the database of objects and scripts etc. made with the construction set. That produces a changefile which the engine can cleverly stream into the final version that the player plays. Most mods do not need additional assets, and a lot of the additional stuff on the PC is centred around resolving mod conflicts etc, which we managed fine without before they became available. The fact that the consoles use the same data engine isn't at all a surprise, given it was initially designed to make the devs lives easier.
What do you mean most mods? Have you actually counted them? No.
Neither have I.
What I have done, though, is played Oblivion and Fallout 3 with and without mods.
In my opinion, the mods that are most interesting - are those that either change the mechanics of the game or add to atmosphere and immersion. The vast majority of the mods I've enjoyed have required FOSE to run, or they've demanded a lot more of the game than the vanilla version. They've also pretty much ALL broken or messed with something in the game - often in a small way, but not always.
Sure, you can have a zillion "quest/item/NPC" mods or modifications to the database. I'm also sure that there are many more smaller mods than there are larger and more interesting mods. That's why the amount of mods that would be feasible is entirely irrelevant.
So, for sure, modding is possible if Beth can make a deal with Microsoft. The problem is, though, that not only would those mods be limited in their nature - they would also have to be either free or be released as DLC. Getting Microsoft to change their entire XBLA infrastructure to accomodate a few games is ludicrously naive. So, it would most likely work just like DLC - where some kind of review process would have to be in place, so that modders could be rewarded for their work. Since money is involved and it would be official DLC - quality assurance is a major factor. So, Beth or someone working for them - would have to assure the game would still work 100% with all mods released in this way.
So it's entirely feasible IMHO. The problem is solely that of getting the changefiles to the users console, which the closed distribution networks would seem to prevent. But I can see a situation where someone loads datafiles into their hard disk somehow (don't know how the file transfers work on consoles). Heck you could probably pretend they were music files, and if the game can play music from the xbox hard disk then it must be able to access the files.
Possible? Sure. Feasible? I don't really think so.
The end result would be entirely different than the fully flexible and open modding scene of the PC - regardless.
So, yeah - we definitely disagree. In fact, I think you're being incredibly naive if you think this is possible in a way that will closely resemble the PC modding community and scene.