I had settled on the later as I wanted to avoid the complicated configuration of WCF, if possible, and just wanted a simple, reliable, and scalable way, to queue messages and process them. Ideally, I wanted a way to host/launch the worker processes from the web app to avoid complicating the development environment by having to install and run separate processes (Windows Service).
I will definitely be looking at this project today and putting it through a PoC.
Update: Forgot to mention ServiceStack in list of frameworks considered.
I've wanted something like this for a very long time.