Wow @Aljoscha thank you so much for this work you're doing here.

It's really important engineering work that no-one else is tackling.

This isn't engineering, it's polemic a proof of concept. hsdt as sketched above is not a good format!.

Maybe we can avoid having to have the one true encoding by using multiformat

Ssb does not need one true encoding, all cypherlinks carry a (free form) hash suffix, which could simply indicate the encoding that was used to compute the hash. And ssb server implementations can talk to each other via morse-code encoded messages if they like - the database doesn't care. No need to switch to multiformats because of this. What we do need is one true logical data model.