A large factor in that is not the technology, it is the glass.
"fastest TB device closest to host" won't make as much of a difference for two factors.
a. stationary ones don't really matter if drop TB display after as that subset of daisy chain is pragmatically stable and fixed.
b. TB v2.0 smooths out the bandwidth so all the TB devices on a single network can get a more even x4 PCI-e worth of bandwidth. So "closest" won't matter as much.
Minor changes ( option that looses the Mag Safe connector and add a port or two of USB 3.0 and/or FW all coupled to the new iMac fused display ) and it would be easy to ship minor variant that was much more effective. The basic LCD panel is OK.
Thanks, excellent info as usual !
It remains to be seen if Apple returns to a more universal approach with its display design; as you said, it requires fairly minor changes .