I think it would be lore-friendly, for the following reasons.
1. In Daggerfall, I think Dreughs were described as the cursed remnants of an ancient, once flourishing, civilization. Vivec is supposed to have ended this civilization.
2. Dreughs are said to have had a city in the Illiac Bay. In the Lessons ov Vivec it's said they inhabitted underwater castles of glass and coral. They seem to have been able to use some language, and even to lie.
3. In the above mentioned Lessons, they are even described as "Altmers of the Sea". However, I haven't found anywhere else mentions which would corroborate any relations with Mers, so, it is likely to be merely a rhetoric phrasing.
4. With the fall of the Tribunal and the withdrawal of Vivec's power, one could consider an hypothetic major hinder for the rebirth of their civilization is now gone.
Well, I don't think we will see any stuff of this kind in Skyrim, but can we hope something like it either in expansions or DLC, or in a further Elder Scrolls game? Let's try to weigh some arguments...
First, a Dreugh Civilization would create many possibilities.
1. It has been hypothesized more than once in these forums that Roscrea could house an expansion. This said, and if Solitude continues to sponsor explorating missions in the Sea of Ghosts, it wouldn't be too astonishing to see a sea-based expansion. In which case, Dreughs are just a step forward, and a Dreugh City would fit pretty well in this context, in my opinion.
2. Moving forward in this direction, it could be possible to see a sea-based faction of seafarers in Solitude. Such factions could add both to gameplay and to the depth of the world.
3. It will be difficult for the devs to fashion creatures which wouldn't seem ridiculously innoxious and unimpressing with comparison to their marvellous dragons. In the deep ocean, however, there can be Krakens and other impressing creatures, which could plead in favour of a sea-based expansions.
4. I have no doubt that a Dreugh City would be an awesome place to visit. Dreugh architecture could be something awesome, and I'm sure that if the devs are to include it, it would be both surprising and memorable.
5. Well, the true potential of the deep waters of Nirn is sttill unlocked...
6. I am sure I am not the only one over here who tends to welcome diversity with a warm heart-true smile. Have you figured how amazing and worthy of awe could be Dreugh armors and tridents? Moreover, Dreugh using them could become very dangerous opponents, especially under water. This could add to Challenge.
7. We could perhaps encounter some of the "clockwork Dreughs" mentioned in the Lessons of Vivec, which seem to be Dreugh-shaped underwater counterparts to the Dwemeri war machines, fashioned by Sotha Sil.
8. If a Dreugh city is in the game, then it could modify drastically Skyrim's (and even Tamriel's) politics. On the first hand, they could put a threat onto commercial navigation, and the other hand, they could be inclined to make agreements with some nation, seeking commercial relationships involving rare ore or Dreugh crafting, and claiming official recognition. Forging such agreements, or eliminating such threats could make very interesting quests.
9. There aren't enough gods in Tamriel (lol) so I want to know the ones Dreughs worship.
But there surely are drawbacks to such an expansion.
1. The whole thing is heavily hypothetic. Some points originate from religious texts whose reliability is subject to questions.
2. Such extensions are the kind of thing which would require much work from the devs; unless they already planned it, one shouldn't hope much in this direction.
3. Perhaps it is the kind of stuff which would deserve a whole game to be treated properly, accurately and completely.
For now, I don't see any other argument, and I'am aware my point is biased. But that's why we are in a forum, a place where biases encounter biases and make children. So, now, let's discuss these (many) points.
Sorry for my bad English (my mothertongue is French) - and for being so verbose (but I was quite inspired while chosing my username)...
PS: I already posted a thread about this but made two mistakes. The first one was to make from it a poll. Easiness of preformated choice discourage discussion. The second one was to put many topics in it, which made my point unclear. I hope it is better this time. However, I am quite worried about this double-posting, and simply removing the previous poll would be unfair since it would be supress people's opinion. I hope you won't find this annoying, but if I break some rule of the forum, please let me know.