I don't understand the need for swappable batteries these days:

Nowadays, if your battery runs out too quickly and you're not near a power socket, you don't need to swap out the battery, you just plug in a portable battery into the USB-C port to charge it back up again.  And, crucially, that portable battery will work with any other laptop/smartphone/tablet that charges with a USB-C port.

In the days of swappable batteries when there wasn't USB-C charging, you couldn't do this.  And if you bought a 2nd battery for a machine, it was typically unique to that machine, resulting in more e-waste when you upgraded.

Furthermore, internal batteries in Thinkpads are easily replaceable.  So, if after two or three years the battery wear is getting a little high, you can easily open it up and replace the battery.

If external removable battery returns to certain Thinkpads such as T14 and T16, this would re-awaken the Thinkpad brand. A new wave of fans will be created.