Model 3 will be critical to Tesla in many ways, but getting all that data for fleet learning is absolutely vital to them. It is their biggest lead over every other autonomous venture out there, so they must provide a way to get that data.
The fact that some customers use it for telemetry and internet access is only the partial reason for its existence.
Data is king
Nobody yet that i've heard of is paying for the network in the car. There have been different ranges quoted for how long its free (4-7 years). But we're past 4 years for some and it's still free. No S is 7 years old yet so time will tell.
The 3, however, could be a different story in terms of the free service.
I did NOT opt for the LTE upgrade. I'm not in a major city area and don't currently commute to one and LTE is pretty spotty in my area.
If Tesla does decide to start charging for the connection, I (and many others I would guess) would just tether the car to my phone. I hate the idea of paying for yet another mobile line, especially when my current one has unlimited data.
I do not believe this will come at a fee. Because of T≡SLA's practice to continuously upgrade the cars OTA, a standard & free data connection is part of their DNA. Relatively speaking, considering the cost of unlimited data plans in most countries (not in the minuscule one I live in now...!) and the sizeable procurement power T≡SLA must have, I don't think it will be any different for Model ≡... IMHO...
I don't see why the updates and data uploads cannot be via WiFi. Do the updates at night while the car is in the garage and store the data until a connection is available. Maps could be stored prior to a trip assuming that you plan your trip in the car the day before. Sure, there are some circumstances when no cell connection would be inconvenient but how does that compare to the cost of the cell connection?
Tesla 'wants' the data from the cars, so can't see them going with less than 3G - and at some point probably not that far from now, 3G will be phased out entirely by the cell providers.
besides the Autopilot data, they also want to have immediate access to the blackbox info that tells them a vehicle was in a wreck and what led up to it. Its been shown to be a pretty good CYA for them in the past when a driver claims the car plowed into the side of a building all on it's own while they had the brake all the way to the floor.