It’s easy to find a TV with USB-C input, though not universal. That still uses the DP protocol, and cables with different connectors on opposite ends are both cheaper and more common than those with HDMI as a result. Also, this is only even an issue if HDMI 2.0 isn’t fast enough for you, so old devices aren’t a concern.
I don’t see “relevance for HDMI” ending anytime soon. Tell me how easy it is to find a TV with DP inputs. Nearly 99% of consumer gear uses HDMI.
It’s easy to find a TV with USB-C input, though not universal. That still uses the DP protocol, and cables with different connectors on opposite ends are both cheaper and more common than those with HDMI as a result. Also, this is only even an issue if HDMI 2.0 isn’t fast enough for you, so old devices aren’t a concern.