I'm sure this is a solvable and solved problem, but I do believe it is non-trivial, and potentially a major headache for a company to implement just to support a tiny niche of users. I'd be delighted to find out I'm wrong though!
And, unfortunately, the business case isn't there, since this weakens lock-in effects. I don't endorse this reason—that's why I run my own HA instance and don't buy or use any products that require the cloud or otherwise can't be operated entirely locally (including flashing Valetudo to my robot vacuum!).