Are the backends supposed to be swappable?

[AntonOfTheWoods]

I just noticed that using memory for testing meant I had code that is invalid for the kafka driver. Basically, memory allows you to have ints as messages, kafka fails when it tries to message.encode('utf8'). postgres doesn't do a .encode but also fails on an int, as does redis.

Is this expected, in that you are supposed to know what your backend supports so you will naturally think to pass the right kind (which is typed as Any)? Might it be worth having an equivalent API (maybe by default, with specific, alternative pub/sub methods that support the full range of objects supported by the platform)?