Even if AlexElec is working out for you at the moment, that will probably be about as far as you can go with the S812. Alex himself doesn't seem to be updating it, at least not as often as he does the 905/912/whatever other hardware he's building it for. I've actually managed to make it run on the now ancient S802 Matricom G-box Q, which is apparently identical to the S812 version, except for not playing H265 video (which I don't anyway) or possibly the wifi chip, which is not an issue as I use the ethernet port.
I'm planning on holding out myself for the next two months or so, and then see if anybody's got some ridiculous "Black Friday"/"Cyber Monday" deals on new hardware. Definitely looking at the RPi 4 rather than another Android box.