The C906 core in Allwinner D1 SoC will make an excellent competitor to the Pi Zero when it ships on the promised $10 to $15 Sipeed and Pine64 boards later in the year -- and that will be a real price where you can buy as many as you want, not the "$5 but you can only buy one" fake Pi Zero price.

The $99 "Nezha" board with the D1 is of course not value-competitive for that performance level. It's a manufacturer's (i.e. Allwinner) prototype board for volume manufacturers such as Pine64 to use to develop software while they work on their own board.

The same goes for the HiFive Unmatched. It's not intended for volume production, it's for developers to use to prepare software for later high volume boards (including the BeagleV).

What you are talking about is drivers for peripherals, which is are SoC-level issues, and really up to the partners (like Allwinner, SiPeed, etc). So far documentation is the most critical part and it's a very mixed bag. I think this will be much like the Arm experience, albeit everyone is at least using device trees these days.