Here's a very interesting but quite realistic proposition:
Warcraft for E:TW.
The main idea of the proposal would be the delivery of the full mod in separate episodes which would each have the feel of a self-contained, complete mod (as opposed to feeling like an incomplete version of the full thing).
The simple solution is to stick with the scopes of the original games, and therefore the first part would consist of just the (purely) orcish Horde and the kingom of Azeroth. Each faction would have a very manageable amount of units to do (though obviously more than in the original games, but consistent to the background), and the rest is simply designing an interesting campaign map for the struggle between these two species.
The mod could probably work well enough with the rest of the game's graphics unchanged, depending on what "medieval" resources are available. A superb soundtrack is obviously readily available.
The next episodes would feature the Tides of Darkness and the Horde's campaign on Lordaeron, including elves, dwarves, trolls and ogres (and goblins) on a much expanded campaign map, as well as options to start in the "Tides of Darkness" campaign directly and combine the two campaigns (if possible, triggered by the fall of Stormwind).
After that, who knows what would be possible with the future installments?
Thus endeth my proposal. Obviously, Blizzard's policy on the use of its IP determines if this is all a pipe dream.
I'm not much of a modder myself, but I wouldn't be against helping in other ways if a project did indeed spring up.