To me write scaling is the main current advantage of KV and document DBs. They can generally do schema evolution fairly easily, but nowadays so can many SQL DBs, with semi-structured column types. Also, you need to keep in mind that KV and document DBs are (mostly) non-relational. The more relational your data, the less likely you are to actually benefit from using those DBs over a relational, SQL DB.
If you have either of those problems, you will know it very clearly.
Also, ironically, Postgres became one of the most scalable NoSQL bases out there, and one of the most flexible to use unstructured data too.
It may not have a very rigid schema, you may later add several other optional fields.
You need very large scale (as in no of concurrent accesses), you want to shard the data by e.g. location. But also, the data is not "critical", your highschool not being visible temporarily for certain users is not an issue.
You mostly use the whole dataset "at the same time", you don't do a lot of WHERE, JOIN on some nested value.
In every other case I would rather reach for postgres with a JSONB column.