I am working on a project that will add considerable new functionality to an existing application. We were previously limited by a framework that did not (realistically) facilitate responsiveness, so everything that was build up until now was not responsive in any way. For the current project we have two seemingly contradictory goals:

 - Integrate our features into the wider application, including a lot of navigation across the different sections (i.e. from old framework to new, and from new to old)
 - Make the new section "responsive"

Frankly, the idea of making the new features fully responsive seems like a terrible idea, since as they navigate through a single application, they would be seeing wildly different views when using smaller devices. Does anyone have any experience in a transition like this? Are there any examples of making certain modules or areas responsive, with the rest not?