re: What replacement phone are you considering or have you already chosen?
Your problem is that you're thinking about the actual capabilities and not money. Qualcomm does this to sell a revision bump as an upgraded design. They are a horrible company in that regard. The 820 can probably do most everything GL ES 3.2 needs to do to run the UI at the high frame rate and refresh speed required, but Qualcomm won't write the software to do it.
Wait. That's pretty much every Android flagship released so far minus the Pixel and Zenfone 3 Deluxe 256GB.
What makes this weirder is that both utilize an Adreno 530. Maybe there are other small changes?
I was under the impression that the 821 is a revised 820 with slightly higher clocks and a revised modem plus other small tweaks.
Your problem is that you're thinking about the actual capabilities and not money. Qualcomm does this to sell a revision bump as an upgraded design. They are a horrible company in that regard. The 820 can probably do most everything GL ES 3.2 needs to do to run the UI at the high frame rate and refresh speed required, but Qualcomm won't write the software to do it.