This is an awesome idea! And the multiple levels of abstraction enrich the concept.

What would be the pricing model?

I also want to give two shout-outs: - the Echoes Chrome Extension that makes it easy to search through conversations: https://echoes.r2bits.com/ - and Tana, of which the supertags reminds me a bit of your user-defined datatype: https://tana.inc/docs/supertags