Hi Henrik,
I have had your same ideas but my experiences are the MS are not at the point yet where the solution you are describing is a useful one. A couple of the reasons not to do what you describe is:
1. Lack of out of the box functionality. As I see it right now, there are not enough out of the box functionality for NAV, CRM and O365 to smoothly work together. I think you have enough work with using two of three to be honest.
2. Price and overlap. When you are speaking of an "all cloud" solution, I expect that you are a small to midsized company. Having both CRM and NAV is both quite costly and it has quite a big overlap in my view. Especiall, if you already use NAV I would not recommend you also buy CRM, unless you are a very big company (and then you probably wouldn't be interested in the all cloud solution at this point).
I think what NPLIMA suggests could be an answer but I think we are kind of saying the same thing. MS is not really there yet but if you really want it to work, with the right partner you can do it yourself. For NAV, having looked at the roadmap here (http://www.insync.co.in/overview-of-microsoft-dynamics-nav-roadmap/) it looks like NAV 9 will be the version where they try to tie it all together.
If you are Swedish and want to pursue the all cloud angle, I can send you info on partners that I have worked with that I think will can help you.
Regards,
Magnus