Hi Simon,
Axon aims to decouple components by providing abstractions for the communication between them. In essence, this means that messages like commands and events are sent over a bus, and the sender doesn't know (nor should care) where the recipient of that message is located.
This is exactly the same for queries. It has been a part of the architecture that has been skipped for a long time, in the belief that it was about command and events, primarily, and queries would be "business as usual".
However, that vision has changed in the last couple of years. Axon is not "just" a CQRS framework, but rather an "Evolutionary Event-Driven Microservices" framework. Queries can follow quite complex patters, way beyond the HTTP-GET-style "hey you, give me this". For example the scatter-gather query (everyone, tell me what you know about ..) or the subscription query (keep me up to date on ...).
That's the goal of the Query Bus.
Hope it makes sense.
Cheers,
Allard
PS. The API doesn't quite work great yet, so we're expecting to make some slight (backwards compatible) changes and additions to it.