This. I basically didn’t use my facebook for the last 6 years and i left it deactivated most of the time. My thinking was that people could use messenger to reach out to me (and my family has mostly been using messenger for stuff anyeay) but even then, that only proved true for a handful of circumstances, and the people who did make use of messenger or a non-deactivated account all had my phone number anyway.
Would my experience be different if I was more active on facebook? Eh, maybe. Maybe I’m an oddity, but most of my high school and college connections barely post on facebook as it is, if at all. I didn’t lose much by finally giving it the axe last week.
Fediverse by design is ideal for institution-based social networks for sure. Each school hosts a server and federates with the nearby institutions (possibly in a limited manner so it’s still focused on your group but you can easily interact with other people from your city)/school district too.
Maybe the school has two servers: one for active students, another for alumni. Some configuration for letting people say “only fill my main feed with stuff from my graduating class +/- 2 years” and so on. When you graduate, you get auto migrated to the next server.
Hometown sort of tries to do this for cities as a Nextdoor replacement (and even nextdoor for a long time tried to keep things hyper local with optional visibility elsewhere until they caved to ad money and NIMBYism)