I’ve seen a couple AK’s chambered for 30 carbine online, they look pretty sharp! along with the AK’s chambered for 7.62x25.
I like the .30 carbine because it allows for a small package, and as per your friend’s Ruger, even dual use in a sidearm and longarm...I’m not sure the practicality of dropping an AK to a (substantially) less powerful round. I suppose at one time, .30 carbine ammo may have been a lot more readily available than 7.62 x 39, but that’s not the case today.