It could have both. The TB monitors using the integrated GPU, and a dedicated GPU with mDP. Though that would just be daft.
No more daft than when older Mac Pros had 2-3 GT120 cards in them.
If the embedded GPU can do OpenCL work then really doesn't matter if some users never "hook it up" to a monitor. Some workload can be shuttled to it that is of added value.
Also no more daft than a server model with a mid-range graphics card in it either. [ with embedded graphics the server model could come without a discrete GPU card opening up another slot for high speed I/O card. ]
What I think folks would get twisted about is if the embedded GPU soaks up an additional slot. For example the Mac Pro went from a 4 PCI-e slot machine to a 3 PCI-e slot machine ( 16x , 4x , 4x with one of the 4x sharing the 4x to TB ). Folks would probably moan at that move.
However, with two E5's that isn't necessary. There are 80 PCI-e lanes. More than enough to allocate 16x to an embedded card and have plenty left over for 4, quite wide , lanes. The design disconnect would only be the single CPU package models. It is more of a pain to add TB to them if it is going to effectively take up 20 PCI-e lanes out of a 40 lane budget.
Maybe it won't have TB at all ?
That's an option too.
Seems contrary to Apple to put in TB and then when you hook up a TB monitor to it, there's no signal.
The gross assumption here is that TB monitors would be primariy device connected to a Mac Pro's TB socket. Especially if there is a perfectly good discrete GPU card in the the PCI-e slot.
No, that is the tail wagging the dog. Mac Pros aren't there to sell TB docking stations ... errr monitors. Perish the thought Apple could actually ship "just a monitor" product. mDP and USB connector and
no power cord. And matte with a wide color gamut. That would be a more natural fit with the Mac Pro. If they could just use a different backlight and supporting electronics it could share the basic panel with the TB version. They could drop the price a bit too. $899 or $799.
The normal mode would
shockingly be to hook the monitor to the discrete PCI-e GPU card just as done now in a Mac Pro.
Daft would be hooking a monitor up to the Mac Pro with a dangling magsafe power connector. It is useless.