Speaking about Panfrost progress: it's really nice to see what those guys achieved during such short period. If they continue their efforts and move to Bitfrost driver (as they stated before), we should be able to run Mesa on latest Amlogic hardware. Though there is one more milestone to reach to get fully open source LE on Amlogic — H.265 10-bit decoder. I would even consider a donation to this goal if there's a fundraiser.
Panfrost is mostly an all-girl effort and she's 17-years old with a very bright future ahead of her. We have been using it for S912 support for 6+ months now and T820 support recently achieved "all green" on mesa dEQP tests which puts it broadly on-part with the ARM blob - and in some performance tests it completely outperforms the closed-source blob. Panfrost has been checking milestones off but the future direction isn't clear at the moment, i.e. whether development will continue to focus on other aspects of midgard support (OpenCL etc.) or whether they'll start to poke bifrost. Mali blobs exist for bifrost though, so there's no rush. Elsewhere in the LE codebase we've just switched our Rockchip images over to lima/panfrost as part of the bump to mainline kernels (no more Linux 4.4 bsp kernel). Allwinner still needs some work before it can make the same switch, but hopefully it will happen in the near future too.
For Amlogic HEVC support is being worked upon, but it's not simple. The original firmware(s) have issues, and there are differences in the software implmentation between GX, G12 and SM1 platforms which complicates everything. I've currently dropped the HEVC driver from my working branch so that content is forced through a software-decode path which at least avoids the hard crashing from missing firmware. FFmpeg still needs rework to accomodate other ecent vdec changes (H264/VP9) but I'm hoping it will be looked at in January to be combined with a Linux 5.5 bump.
VIM3L is already supported in my working tree so other SM1 (S905X3) devices should be reasonably simple to add support for.