the concern is that dbt-core will become stagnant.

It basically already has since they started developing dbt Fusion, so in that respect this probably doesn’t change much.

I expect they’ll keep developing Fusion but possibly as even more of a commercial-only offering than it already was.

What's the problem specifically? Are you banking on some future features? Can't fix the bugs yourself? Worried it won't be compatible with future data warehouses?

I know people don't like it these days, but you can just continue to run old software.

dbt in particular is effectively useless without maintained and up-to-date connectors to your particular database.

Do your database vendors often do breaking changes to their protocols? dbt just generates SQL and that's not going anywhere.