Well, apart from the lack of LTE connectivity. Please, anyone@apple.com, deliver me from the temptation to get another ThinkPad, just because they ship WWAN...
I have two unused SIMs with unlimited data (Thank you, Sprint/T-Mobile free line promotions), and would love to be able to put one to use.
(Edited to add: one of the great things about a MacBook [Air] is supposed to be that you just throw them in your backpack, and you can be productive, like, anywhere, without having to worry about battery life, or anything. Still, 'lack of connectivity' kinda kills that dream, which means I still carry my ThinkPad T14 gen3 (despite its power management flaws) or Surface Go2 (Potato Inside<tm>), where I would rather take my MacBook)
Also, I noticed a while back that connecting to the iPhone with a USB-C-to-Lightning cable got me a hardwired hotspot.
iPhone and iPad tethering works extremely well. I've spent many days working via tethering and in practice it's just as good as having a card in the laptop IMO, other than a minor pause in connectivity when you open the laptop. Plus it's much cheaper.
It would be nice if they added a built-in option for people for whom money is truly no object, but it really is not a limitation that every impacts my in any significant way.