My solution to this problem would be legislation that allows customers, if they wish to, to return devices for a full refund if the company that manufactures the device makes a change that removes functionality that the customer valued. This doesn't prevent the company from making the change, it simply makes sure that they incur a cost for doing so, and it makes whole any customer affected by the change.
This basically means that everything that has software updates can be returned forever. Like most of things in life, the answer is very rarely a new myopic and ill-conceived law added to the thick stack of existing incomprehensible legislation.
It doesn't. It means that functionality cannot be changed in a degrading way, but upgrading and non-conflicting security updates are still allowed.
For a customer, money upfront and money over time is the same (adjusting for the interest rate). They don't need just a dead brick, whatever it costs in production. When your saas stops having a feature, you stop paying. This is no different, except that I'd vote for a law which amortized the upfront cost to the real usage time. E.g. I bought a treadmill with 2-year warranty for $4000 and it stopped doing a claimed feature after a year (iow, became broken from my perspective). I either receive a service which returns the feature, or get $2000 back + 20% fine for inconvenience.