They won't don a werewolf dlc they already have Tribunal for morrowind and Bethesda would never in a right mind repeat a DLC subject. Also another vampire DLC would be cliche.
First of all, the Tribunal expansion had nothing to do with werewolves (you're thinking of the Bloodmoon expansion), and secondly, they have more or less already repeated subjects in DLC. For example,
Spoiler the Tribunal expansion dealt with sinister gods (or in this case "false gods," though they were more or less gods, but mainly because of a certain artifact), and Shivering Isles dealt with sinister gods as well.
Now, repeating the more specific subjects like using the same (or extremely similar) characters, lands, story arcs, etc., THAT is something that they would not do. In other words, some subjects (generally vague subjects like new armor or new "creatures") will inevitably be re-explored, but certain elements like specific characters and events are likely to be avoided,
Spoiler like another Bloodmoon Prophesy focused expansion, for example.
In other words, their focus is on doing new content based on lore, without retreading the stuff they've already done recently too much.
Now I don't know if they really need to do a werewolf-centric expansion for Skyrim since I think that would be better suited for a game that does much less for werewolves (like in the cases of Morrowind and Oblivion, which had none, and for some reason werewolves were never added officially into Oblivion), but they can add on to werewolves more as side content in future DLC. Werebears are a little bit of a different matter than werewolves, since they don't yet exist officially in Skyrim.
I agree, maybe Bethesda could add a "werewolf customization screen" which would look similar to the character customization at the beginning of the game and would pop up immediatly when become werewolf. Hopefully beth will add this feature along with werebears, spears, lunar transformations and the option to contract sanies lupinus from wild werewolves in a DLC that takes place in the Hunting grounds.
I agree with what you say. I think a lot of what you say would go over decently well, except for those people who think lunar transformations should never be done ever again even if it's limited to specific strains of the lycanthropic curse. I don't understand that mentality at all. I think lunar transformations should exist for the people who want it.