I'd rather see them re-tune the old 40s for 10 and 25 mans.

Then again, 40 mans did feel more epic than 25 mans.

I think maybe as a new dungeon difficulty, but then again the gear gap between 10 and 40 man raids would be reasonably large.

Have one difficulty setting for 10 mans, one for 25 mans and one for 40 mans, so that people can choose to do it in a small group, in a larger group or like it was before the Burning Crusade.

I think the idealistic concept of a 40 man raid is far better than the practicality.

40 mans:
epic, yes
Challenging, yes
a supreme pain in the ass, you better believe it

I never knew what it was like back in the day, but from what I hear, most of the dungeons didnt need 40 people, only 30 as ~10 of them were more or less AFK.
And has anyone tried to coordinate a city raid lately? Its nearly impossible to get them all going in the same direction.
Finally there is the point of what would happen to raiding if only the large guilds could raid on small servers? Many guilds would fall apart, and you would end up having 3-4 super guilds, at least on my server.