AGPL is contagious I heard, seems quite dangerous to ppl planning to make preparatory software bolted onto an open source core.

That's wrong. Licenses are not bacteria.

First, AGPL only requires to release changes ONLY to the existing AGPL codebase and ONLY if you are providing it as a network service.

Second, the whole idea of virality is a huge misnomer. There is no such thing as one thing "infecting" another in copyright law. GPL/AGPL cannot magically make another piece of software change license.