Agreed. So first have a Mac that is ready for 4K @ 60, then purchase the monitor. If not, upgrade the Mac before getting the monitor.
You might want to wait until WWDC next month to see what Apple says about when they will move to the Skylake series of processors and chipsets. Those will introduce TB3 which will support 5k over a single cable. That sets the stage for having a updated Thunderbolt Display doing 5k over TB3 with the new Skylake based Macs. It could also mean that Macs that can do 4k today at 60 could also do 4K at 60 via TB2 towards the new Apple Display. So Apple would have a market for such a monitor.
I would love to replace my Thunderbolt display with one doing 4K via TB2.