Actually, nest was already bought by Google a few years(?) back.
It was kinda bound to happen, though this soon (they did promise nothing would change) is kinda weird.
Myself also have a nest thermostat and love(d) it to bits as it pretty much always worked.
It will still keep working of course, just 3rd party apps/devices will not be able to read or write to it, that includes homey, and any other automation thing, even IFTTT will stop working as they make use of the same api’s
Logitech tried to do the same with their harmony hub, but had so much backlash that they partially changed their minds.
Not so sure Google will do the same though.
I do appreciate athom actually taking the time to let their users know immediately when it became announced, and offer an option, it is of course only 1 option of which there are many.