Bingo! They could "sunset" Fi on a whim when they get bored. Plus Google's poor record of customer service or rather AI Bot customer service - is what will keep away me from trying it.
"Poor record" is actually not my experience. Customer service with Fi and Google Store is pretty excellent. A lot of people in my network also have the same good experience.
I've been on Fi for 4 years, and it has been a very flexible, positive experience vs. the alternatives at that time. Even if they were to sunset it, I don't particularly see the risk; I would just change to another service.
Fi customer service is actually excellent. First level support is actually knowledgeable and trying to help you, as opposed to just being a wall trying to prevent you from reaching second level support. Also the wait times have never been more than 2-3 minutes for me.