All I would really want at this point is support for dual double-sided 2280 SSDs, and upgradeable RAM. The thickness may have to increase a bit, but I can take additional battery life alongside that.
Optionally, the entire motherboard could be swappable as well, but I know at that point this computer would be viewed as an absolute fantasy.
Before anyone else comments, I know the first two requests sound a little ridiculous as well, but people also thought the same for upgradeable SSDs not being possible in tablets as well and look where we are today.
If the RAM sticks at the current compact laptop size are not small enough, perhaps the industry should work on a smaller, more compact standard that helps retain that degree of upgradeability.*
Finding a 2230-sized SSD is a challenge and at this time capped at 1TB (once I can upgrade to a 2+TB I'll forget about this post), It would have been nicer if it was compatible with a more common form factor, I would have loved seeing 2280 as an option. I do wonder if performance is better/worse if it had been (temperature-wise). Anyway still bought one for entertainment while on the road/traveling. I'm very happy with it and hope to enjoy it for many years to come.