Indeed that sounds like a fantastic machine. But still doesn't meets my battery goals. I really think that some of these mobile-soc-in-a-laptop devices should utilize the extra space they have and add on an extra battery. This one seems to have 45Whr. making it 99+WHr would have been much better IMO.

you would need the old Thinkpad with hot swappable batteries, I would say it's a shame they stopping doing them but I don't actually think many people used them in practice.

Also now you can do pretty much that with a separate powerbank charging your laptop via usb C. it's more cumbersome but with a more universal interface and more versatile.

You don't need hot swappable batteries anymore. Tuxedo infinity book packs in a 99Whr battery in a thin form https://www.tuxedocomputers.com/en/TUXEDO-InfinityBook-Pro-1...

If they ever put a mobile SoC in a 13 incher with that battery, I would happily buy it.

You could make a custom battery. I've done this for an e-bike to extend the range considerably.