So, I just updated (added to) my 3 Speedlite 500 EX's with 2 600EX-RT's and the on camera controller, since the price seems to be dropping. But, why is the price dropping? I'm planning on getting a 5D MK4 or new 1dx when they come out, and, I now wondering if the new bodies will add something cool that will obsolete the 600 EX-RT's.
I don't think there could be anything added to the bodies that will obsolete the 600EX-RT. Its main strength is the ability to use it off camera.
On the other hand, they may add an integrated trigger that would send the ST-E3-RT to the bone yard. That would be fine by me. Especially if they add an onboard focus assist beam too.
I've got seven 600EX-RTs. I think they will work just fine for several years.