Hi,
I wonder if it is possible to go for an "all-in" on the online strategy, having 2013 hosted (is MS going to do this - like CRM online + office 365
Yes, with a slight twist. My company has been involved in this kind of setup and we've found that it will work much better if you host CRM and NAV 2013 in the same servers rather than using a "pure cloud" setup.
So you'll need VMs for NAV, CRM, and SQL server. This can be hosted and license can be subscription-based.