Its an interesting question. I think you will find that manageable. The part that challenges the traditional solution model is that now if you make changes to one of underlying solutions, you have to change the app solution as well. I guess the other way to do it is to put the app in all of the solutions so that if you change that solution, you can change the app in that solution. The app really lives on its own in each environment as a single app, so it should stay up to date across solutions, but I haven't verified that behavior in real life.
After thinking about this some more, I'm not sure that in either case you will be able to change two base solutions in ways that affect the app at the same time, safely.
In the App Isolated case, if you are making solution changes to two of your base solutions, the app solution can't be deployed until both base solutions are deployed. Or another way to say that is that you can only change one base solution at a time if you want a clear dependency path.
In the App in All case, you're going to run into the same problem because there's really only one App. Although your changes "should" technically be isolated by solution, when you go to export the App in one solution it is still going to have all of the other solution's dependencies attached to it.
Cool problem. Let me know how you solve it.
Brett
