We would like to confirm that it's there in our roadmap and will do the best to bring you at the earliest.
However, it's also worth to mention here that AV1 is still under early development and none of the devices provides the hardware acceleration for the same. And, the existing software-based decoders are highly inefficient as they are not optimized to work on mobile devices. So, even if we implement that it will be barely usable.
It will be usable since some low-end 160p-240p-320p or 15fps reencode can already be done at reasonable speed on 5-year old PC now.
And this makes some space-sensitive video storage already possible with old devices.
It is the same story as i can still use Galaxy S3 to show our family ex-VHS 480p videos to my grandma at 2.5Mbits HEVC per second, full software decoding with MX!
And on S2 can do 500-800 Kbit HEVC 16:9 480p no problem as well.
Back to AV1, If S3 would handle 480p 30fps at 500kbit AV1 full-software it would be still perfect viewing experience for such a small screen or a MHL+TV+grandma
I have been using Mx Player Pro for several years, with custom codecs addon, and been very satisfied by this app since. The latest UI is very pleasant, I find.
Did you notice, please, that dav1d has been optimized for ARM and ARM64 since 0.2.0 version ?
As it is already supported by ffmpeg, it seems feasible to add this decoder to Mx Player also ? Of course, a budget smartphone will not be able to decode UHD videos as a modern desktop CPU can, but HD and even FHD 25fps might be reachable on a middle range device ?