That is absolutely possible. In fact, the idea of designing an application as a set of modules (bundles) fits very well with integration applications. There are a number of options when deciding what to expose as the OSGi 'services' ('references' on the other side). For example, the Spring Integration MessageChannel, as an abstraction itself, would provide very loose coupling between bundles.
In any case, we would be very interested in hearing more about the approach that you take if you do decide to pursue this. I would also highly recommend considering dm Server (
http://www.springsource.com/products/suite/dmserver).