In short: Hell yes!!
To elaborate: I know another server that did something similar and it worked out fantastically. Also, aren't you guys planning on making PoWar tier 6 or is that on the back burner now? In order to do that, wouldn't you need custom files for models?
Anyway, I had been hoping for this since my first week on the server. I never brought it up because I wasn't sure if it was too difficult tbh, but it would add even more uniqueness to the server. Some people hate more customization, others love it. If you're on THF, you must love it though, so I say bring on anything you can customize!
Edit: Reading Xeb's post, I don't think you could ever break the EQ feel unless you changed classes and everything. I don't think they'd be able to make completely new models (or would you?), as far as I know they'd just be able to make normal EQ mobs in their non-natural zones. For example, there are only a handful of "global" models to choose from. When not using global, you're stuck with zone-specific models. That's why if you tried to spawn a dragon in the nexus he'd come out a human

Fortunately, to make him actually be a dragon it's just a matter of modifying a few files...