Combining logic chips into the same wafer such that no motherboard is needed is just a matter of wafer size, owning/experience with the IP, and needing connectors for IO like speakers, mic, camera, etc. All trivial to do if you're willing to take on the costs of (or reduce) poor yield and less repair-ability. This is the current trend even for chips in AWS like Graviton.
Silicon Substrate for OLED: https://arstechnica.com/science/2020/03/blinkin-fast-oled-ma...
Details of TSLA's push to make batteries part of the device body. https://www.forbes.com/sites/jamesmorris/2020/09/22/tesla-re...