Love to see the Tholians on the big screen- not just one in captivity but cities of them. The asteroid base we saw in Enterprise looked far too conventional, if you go by their ship design and physiology you could have some really interesting designs...
Although not stated, I had the feeling the Tholians had captured that base from someone else. I agree there is a lot of scope for some great designs, although given their physiology Kirk will never confront a Tholian face-to-face.
Kirk never met face to face the Romulan Commander in 'Balance of Terror' or Khan in TWoK so you could have a great confrontation/resolution without being in the same room.
Not only do the Tholians have a bizarre physiology, but they are also interesting as a people- very territorial, technologically advanced, methodical and willing to give an enemy a chance if they are honorable.
I just hope it is a good alien race they depict, not an interchangeable villain with tattoos or facial makeup.