Which is useful for early prototyping I guess, but does it have any way of interfacing to non-HDMI screens? You wouldn't want to use HDMI for a product, and even for DIY hobbyist stuff it's probably not ideal; small HDMI screens with touch are exotic, expensive, and not all that small.
Is there any reason they'll remain exotic, expensive and not that small? (I don't know what interface the typical high-dpi oled touch screens use, like the ones you find on a Galaxy Note 4 etc) -- but it seems that HDMI might make perfect sense for a tiny 4k screen (and it seems reasonable those will become more and more common)?
Devices don't use HDMI to talk to their built-in screens due to licensing fees, complexity, etc. Usually it's either LVDS or embedded DisplayPort these days, with newer/4K screens being more likely to use DisplayPort and older ones generally using LVDS.
