Microsoft doesn't get a cent for any microSD/HC/XC card slot, since they didn't invented it, or the cards to go along with it. Toshiba did.
You may be confusing the issue with the type of file system in which said card can be formatted. The most common (for capacities above 2GB anyway) is FAT32, designed by Microsoft. Google could simply use any of the excellent Linux alternatives like Ext4 instead, a far more powerful file system.
But really, it is of Google's (and Microsoft's as well) best interests to push for online services and storage, since that ties you to their overall platform ecosystem for the long term. So, lack of local storage expansion is not a mere possibility, it is just a matter of when, really.