Handwriting (in and out) support is very important IMO. Also being able to draw DAGs.
I'd like an e-ink device with high frame rate and HW powerful enough to run some models locally or with good enough connectivity and sensors that e.g. Computer Vision tasks can be offloaded to the users' smartphone.
Feel free to expose your ideas on there :) I welcome Open Source discussion!
Even these orders of magnitude are correct, this is still 14t-438t of material to process /per day/ just for one person.