When you start talking about it like that you end up going in circles really.
For the most part any hero that showed up in Warcraft 3 you expect to look somewhat similar in World of Warcraft, this wasn't as possible in release of classic, Thrall using a normal Orc model, Jaina losing those wicked eyes, etc.
When Maiev was introduced in BC, along with Illidan, Kael, Vashj, her model was very very similar to what you saw in WC3. Hence, saying she had a unique model.
Many bosses in the game are rehashes of old bosses we've seen before. Kel'Thuzad for instance looks like every other Lich in the game. Every undead dog post Naxxramas looks like Gluth, etc. On occasion you get a unique models like Thaddius(at the time), or Grobbulus, or Lotheb. Most of the time you only get these new/unique models as bosses in new raids. If Bolvar is indeed the flaming man we saw before, he would be one of the very few heroes/side NPCs that's not an actual boss to get a unique model just for 1 instance.
WoW Evolution is an interesting thing, hopefully Thrall gets a new model before he steps out as the Warchief.

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I still miss the eyes.