Thinking about it more, there's no down side to DP. Every card manufacturer should spend an extra $2 and ship with a DP -> HDMI adapter and drop HDMI universally. There's no down side. And that $2 will be well worth the licensing fees they don't have to pay, and the software they don't have to write.

An adapter that supports HDMI 2.1 will cost way more than $2 and its price will also need to include the licensing fee so you don't get around that.

Even if it isn't 2.1, the off the shelf adapters will definitely cost, but it is a long-term strategy. If every card supports DP natively and everyone is shipping hdmi 2.0 adapters, monitor manufacturers will be strongly inclined to include a native DP port everywhere, no more HDMI only devices, including potentially TVs. At that point the card manufacturers stop shipping with the dongle.

To bad my card can only do DP 1.4a but can theorectically do HDMI 2.1 - but can't under Linux.