On HDMI things that don't exist
I'm the maintainer of several headless servers that very ocassionally need to have a screen attached to them for special cases like boot errors or BIOS tweaking or the like. For this, I need to keep around a fucking screen monitor that is cumbersome and heavy and tedious and serve no other purpose while idle. Instead, tablets (that usually have screens with acceptable size and quality) should include a HDMI input socket that, when plugged, made it to behave like a common monitor.
On the other hand, TV sets are no longer just gadgets that receive signals and convert them to pictures and sounds to be fed to couch potatos. Internally they are computers that also generate content via its internal apps like Netflix and Prime Video and whatever, so they should include a HDMI output socket to connect, for example, another TV in the other side of the room or a projector.
Computers should also have the HDMI input socket mentioned above, as well as reverse-USB connectors for using its keyboard and mouse to control external equipment. This way, a simple laptop could be used as a portable KVM without the stupidly expensive gadgets that are common in server farms.
I don't think any of these features would make equipment much more expensive nor complicated.
Build these things and I'll buy them.