As USB-C becomes more and more ubiquitous, I'd love to see every device with a USB-C port and a display to support incoming DisplayPort alternate mode. That would be a worthy successor to Apples target display mode and would offer a great way for using devices like tablets as secondary displays.
That would be super expensive from an electrical BOM point of view. Laptops and phones are simply not designed to input video. Closest you might get is USB gadget (also pretty tricky) and do display over that (ala displaylink).
I wonder if reconfigurable FPGAs could be the answer? They could be reprogrammed at runtime to hardware-accelerate whatever the host system wants without having to waste space on discrete hardware around for use-cases that may never be required by the host system.
For many displays you can buy relatively simple controller boards from AliExpress that take HDMI or similar. They can be a great for reusing old laptop hardware that you no longer use.
I don't think manufacturers will bother implementing extra hardware just in case their devices die on you. It'd be great, but it's very much a niche use case.
