I think shooting my AR-15's in 223/5.56 is kind of boring. I can't imagine shooting a .22LR AR-15. It would totally be a visit to Snoresville, USA.
I do have a Ruger 10/22 and one of Ruger's new 25 round magazines. It is "OK" to shoot once in a while, like once every five or ten years. An AR in .22LR is a complete waste of money, as far as I am concerned.
Learning to properly operate an AR in 223/5.56 is not so difficult that one needs a .22LR version of it to afford the "practice time". They don't exactly give these .22LR AR-15's away for free. You can buy a lot of 223 ammo for the cost of a .22LR AR-15. That's the silliest argument for a .22LR AR-15 that I've read anywhere.
I'll go one step further with this (one step further...than I probably should...)
I've got a Daisy BB rifle that is shaped like a Winchester model 94. I'd rather take that down to the basement and shoot that thing for a while than go to the range and shoot a .22 that I need to go home and take apart and clean.