How to interpose RabbitMQ between REST client and (Python) REST server?
I would recommend switching wsgi to asgi(nginx can help here), Im not sure why you think rabbitmq is the solution to your problem, as nothing you described seems like that would be solved by using this method.
asgi is not supported by apache as far as I know, but it allows the server to go do work, and while its working it can continue to service new requests that come in. (gross over simplification)
If for whatever reason you really want to use job workers (rabbitmq, etc) then I would suggest returning to the user a "token" (really just the job_id) and then they can call with that token, and it will report back either the current job status or the result
If I develop a REST service hosted in Apache and a Python plugin which services GET, PUT, DELETE, PATCH; and this service is consumed by an Angular client (or other REST interacting browser technology).  Then how do I make it scale-able with RabbitMQ (AMQP)?  
Potential Solution #1

Multiple Apache's still faces off against the browser's HTTP calls.
Each Apache instance uses an AMQP plugin and then posts message to a queue
Python microservices monitor a queue and pull a message, service it and return response
Response passed back to Apache plugin, in turn Apache generates the HTTP response 

Does this mean the Python microservice no longer has any HTTP server code at all.  This will change that component a lot.  Perhaps best to decide upfront if you want to use this pattern as it seems it would be a task to rip out any HTTP server code.
Other potential solutions?  I am genuinely puzzled as to how we're supposed to take a classic REST server component and upgrade it to be scale-able with RabbitMQ/AMQP with minimal disruption.