> The 16" still lists 100Wh

For those not aware, the 100Wh limitation is not Apple, but imposed on them by the airline industry (IATA)[1]

Anything over >100Wh && <160Wh requires airline approval at individual passenger level. Anything >160Wh is classified as dangerous goods and must be prepared and packaged correctly and put in the hold.

[1] https://www.iata.org/contentassets/6fea26dd84d24b26a7a1fd578...

It would be cool if they had an add on battery that fit seamlessly. Or imagine a swappable battery? And then ensure you only use the 100wh when flying?

The airline rules are a bit arbitrary. They have allowances for mobility devices but don't seem to take any extra precautions for them when they have bigger batteries. There are still a lot of dangerous gaps in airline safety when it comes to lithium batteries.