It's prototypish in a way that it combines old (the headstock and the frontjack) and new (the TB Plus pups). Kind of the missing link between the 1986 Japan run, which was still very Bicentennial, and the regular new Birds in late 1987. I guess that on the basis of these Custom Shop babies they decided to downsize the headstock and move the front jack to the side - both of which, if I may voice a minority opinion, I thought to be progression. You see a lot fewer of the new ones with broken headstocks and they are less neckheavy too. I know, purists will disagree. And I find side jacks much preferable to front ones - I've ripped out the entrails of front jack basses a couple of times in my bass playing life, but it has never happened to me with a side jack.
That said, after 25 years in service, the current TB IV could use some revamping and I don't mean change of hardware from black to chrome, that is just cosmetics. They could gently deepen the cutaway, try some different pups in different positions (or just put one in a sweet spot as a rejuvenated TB II), offer a three pup model (TB III anyone?) etc.