erbas the main influence is the ffmpeg changes the Raspberry Pi foundation devs have been doing on stateful V4L2 support. I'm tracking the work but beyond a point in mid-December the changes to ffmpeg need corresponding changes in the vdec drvier and this is beyond my non-coding abilities to do .. and since nobody else works on this we're stalled and unable to keep up. H264 is now working well on Pi hardware.
I'm also using updated firmware, but updated is not always better since Amlogic does not backwards test on older hardware they no longer support so change that fix e.g. GXL may also regress GXBB, and testing that is a hugely time intesive task (and work is busy).
In other news, I now have mainline u-boot booting a WP2 (GXBB) box from SD card (after erasing vendor u-boot from emmc) and have been using it as the family daily-driver for the last week. I'm currently trying to understand why audio must be forced to 44.1KHz to get audio output while the same kernel image on a GXL/GXM device is fine. However I'm at the limits of my non-coding-developer knowledge so progress comes only from guesswork and trial/error testing which is time consuming.
For the wider audience: I added a Minix Neo U9-H (S912) device tree to the "box" image based on educated guesswork and the vendor kernel device tree. It would be nice if someone with that box could test it and give feedback.