The GPU driver itself is largely the same, though it might need some tweaks for the specific variant in the K1.

The bigger hurdle will likely be the display controller. The TH1520 and JH7110 both use the Verisilicon DC8200, whereas the Spacemit K1 uses a custom display controller that will need its own DRM driver mainlined.

The Orange Pi RV2 (Ky X1) uses the Imagination BXE-2-32.

The good news is that firmware is available for that variant. The bad news is that Mesa currently lists the BXE-2-32 as 'unsupported / not under active development' (unlike the BXS-4-64 in the TH1520, which is active). https://docs.mesa3d.org/drivers/powervr.html

So while the kernel driver (drm/imagination) is the right path, the RV2 is a steeper hill to climb: it needs the SoC kernel plumbing and likely some work in Mesa.

I agree DisplayPort would be nice, but unfortunately, almost all currently available RISC-V SBCs only have physical HDMI and MIPI DSI connectors. We have to support the hardware that actually exists on the board.

If your board comes with a HDMI output you surely want to the that to connect e.g. a TV