With the current NServiceBus architecture, Azure Functions are not compatible with the conventional NServiceBus endpoints. Typical endpoints are more suitable for long-running message processing. Azure Functions are good to get something in/out with short execution time and bursty load. Azure Functions hosting model is currently not supported by NServiceBus, and due to Functions opinionated API, many features will never be compatible (delayed recoverability for example). Additional issue with Functions is that certain behaviors are dependent on the trigger type. Failed messages for example, for ASB those are dead-lettered. For ASQ failed messages will be moved to various <originalqueue>-poison queues.
We currently have a survey about Azure Functions going on. I would encourage to participate if you have feedback.