Putting a rechargeable, non replaceable lithium battery in a new version of a device that used AA before is not an upgrade.
Modern rechargeable AAs are cheap and last plenty long enough. And even if the lithium battery was replaceable, it will often be an unneeded proprietary change that'll cost more than it should.
Standardized replaceable lithium batteries should become the norm really. I get why you don't want the average person messing with an 18650, but you could make packages that have decent protection circuitry, that stuff is so cheap these days.
@seatsea yes! whenever people complain about xbox controllers using AAs I go "nooo I love just slapping a pair of rechargeables in it and it works"
@noiob Occasionally yes XD