I prefer to have an e-waste law that says that if you stop maintaining the service, you have to open-source it :)
(That's before the blindingly obvious observation that even something provided by the government at no cost at point of use has a cost which is ultimately borne by the people.)
I think we'd also need to figure out some durable and stable way to reach a conclusion on "when should the software be published out of escrow?" that handles a bunch of the various edge cases. "What happens to devices that are one-time programmable? What devices are in-scope/out-of-scope? Does this apply to radio firmware as well as general CPU firmware? Is the software license changed alongside the release of code from escrow? Are signing keys also released? Is code released from escrow just because some individual use case is no longer supported by the mainline firmware? [Is a disagreement with a product decision enough to release the old code?]"
It's too expensive and too unlikely to succeed, but I could sue Chamberlain now arguing that they have breached an implied contract and that the remedy I seek is for them to open-source their code.
Best case, I think you'd get your purchase price back. I'm not sure how you'd argue that remedy is insufficient, either - hence why my preference is to have the cause of action written into the law we're imagining here. It'd be even better if we can write in that the remedy for a degradation of the service is an open mechanism by which the user has sufficient level of control as to recreate their desired functionality.
The second year there is much less work but they double the cost. You go along with that as it takes a lot of work on your part to engage a new escrow firm from scratch.
The next year they double it again. It's still demanded by your large corporate customers and you try to pass on the costs but they don't want to pay it.