hey!
Oli here from the WorldBrain.io team
Yes we are in close contact with the Hypothes.is team and may develop some shared components in the future. We already use their anchoring library.
Internally we don't store the annotations in W3C standard yet, but will provide that as soon as we get to develop the ability to export or access annotations via an API.
How do you imagine Memex being used as a backend in your context? Once we offer more integrations to other services, it is definitely thinkable to also make annotations from Hypothes.is searchable. Is that something along the lines you're thinking of?
Cheers! Oli