Currently our main focus is on Yocto, since this is what most people would use in production. Right now BSP runs on 4.15 and the processor is well supported in mainline. Since our own product is based on Neutis we put a lot of effort in testing of stability of the system and peripherals.
Sorry, it is the middle of the night here and I am not ready to confirm on the exact Debian version, but I believe that it has not been decided yet. You can contact us directly and we will get back to you with more info on this.
There is so much work done by the great linux-sunxi community, you can see the mainlining progress for H5 processor here: http://linux-sunxi.org/Linux_mainlining_effort
Sorry, it is the middle of the night here and I am not ready to confirm on the exact Debian version, but I believe that it has not been decided yet. You can contact us directly and we will get back to you with more info on this.