I don't think bitcoin ATM is a good idea because we all have bitcoins in our mobile phones then why we need to go to ATM?
If we want to buy bitcoins also it can be done in the internet by just sitting in the home,bitcoin machine is very expensive equipment so you need huge investment for it.
maybe the reason OP is the thing we do that related to the internet will allow loss of signal from the internet which can happen anytime and of course it will be very disturbing in terms of bitcoin transactions. and that I know as usual in making transfers or withdrawals we do by using ATMs it does not have to use the internet network, and that's just my opinion if there is a mistake I say please you can straighten it.