Other manufacturers often charge smaller amounts for extras like heated steering wheels, matts, car play etc... I also see Tesla wanting to have as few options as possible so they can sell cars on boats as they currently do.
So the software provides a way of doing both, providing options but charging extra if needed. And the subscriptions is the next step to make it seem cheap enough.
I guess the big big big problem, is the perceived or expectation that a car that cost quite a lot of money already doesn't come with something quite basic, and more money is needed as a consequence.
Personally, I already think the extra £10 a month for full connectivity on a model 3 is a bit on the steep side compared to data only sims available (which in essence is what it is), if they do the same with other options like heated steering wheels, then I doubt I'd buy for anything but the coldest couple of months of the year.
But that is also where the strength of something like that an a monthly subscription works well, pay for it only when you need/use it. The price still needs to be right though.