[phire]

The main advantage of the SIO TMDS encoder, is that it allows you to output TMDS on any GPIO, instead of the eight that the HSTX is restricted to.

And they allow an easy upgrade path for projects that were already bit-banging DVI on the rp2040. Other than those two advantages, I don't think there is any advantage to the SIO TMDS encoder over the HSTX TMDS encoder.

I get the impression that the SIO TMDS encoder was added to the design first, and there wasn't a good reason to remove them after the introduction of HSTX.