Looking for additional revenue sources isn't a bad idea, but charging for premium access is likely to annoy the community to a degree that will make the great Visual Editor revolt look like some quiet and polite murmuring.
That's definitely a conversation worth having, as it helps us understand what we want to do, and who we want to be.
Do we want to charge for knowledge? Of course not. But do we want to be able to introduce cool new tools for everyone faster, because e.g. Google is willing to pay for their development if they can use it for some time earlier as "premium"? I don't know yet. Let's talk.
I don't intuitively object to Google paying for some additional features, they ride on the back of our content in many situations, and we don't even know how many people see it (content is cached).
I do, however, believe that if we ever decide to do this, with the community's backing, any charging should resemble grants a bit (there should be a clear time horizon when what we are able to develop as " premium" becomes standard and free; if it is also useful for the general public).
Best,
Dj