I don't really know about UniPro and I'm learning about it as the discussion goes, but one of the point listed on Wikipedia is "reliability - data errors detected and correctable via retransmission"
This is where CPC could come in, probably with a different name and a reduced scope, as a way to implement reliable transmission over UART, SPI, SDIO, by ensuring data errors are detected and packets retransmitted if necessary, and be limited to that.
You mentioned HDLC in the past. What is interesting is that HDLC is actually used in Greybus:
https://elixir.bootlin.com/linux/v6.15-rc7/source/drivers/greybus/gb-beaglep...
I've no idea if its just for framing, or if there is also retries on errors, S-frames with flow and error control etc. There might be code you can reuse here.
Andrew