Highly doubtful. The next TB display will probably be announced alongside the new Mac Pro's. No need for a GPU there! Besides, GPU's are outdated quickly and Apple probably doesn't want to launch a "new" TB display every year.
You know that those cards are replaceable, and that the Thunderbolt-to-PCIe bridge won't likely outdate, no?
You could probably even fit regular PCIe cards, as the space isles constrained as in the iMac.
The problem would be to sell iMacs instead of Mac Minis with Thunderbolt displays, not the technology or distribution. You could even build those completely passive cooled, if you use the stack effect and the aluminum back as a heatsink.