Well for this kind of camera, a build in SIM reader are a must, the current model of needing a wifi AP in the car are silly.
But it is a okay way to save events, but having all video go that route i think would be stupid, and expensive.
A subscription for unlimited 4G data here in Denmark still cost 33 USD/mo, but only a couple of providers have that, then you drop down to big data 500 - 1000 GB/mo but the price are more or less the same.
I would prefer to just backup events that way, if only i could get a clone of my sim card ( which i can not ), cuz i have 30 GB/mo and i only use like 3 with the phone, so the rest would be nice to share with a camera.