It’s flexible for you, not for the customer.

When a person buys a new phone, it’s a new product. Your product is the same experience that they will have to pay multiple times for if they simply change their phone.

It is user hostile and gives the customer the impression that what they are buying already has an expiry date, and not in a good way.

Why don’t you have an option to provide X years of updates, and after that they will have to buy a new license for the latest capabilities and features? That’s more fair, since users won’t have to be punished for buying a new device.