Academia should now be considered a conglomerate of business corporations, dedicated primarily to increasing profits and income and cutting costs.
Like other corps there's a trend towards increasing perceptions of value by marketing mediocre products and experiences to death, rather than providing actual social value with products and relationships that are truly inspiringly awesome.
So I don't think the current model is sustainable. It won't collapse next week, but I'd be surprised if we're still here twenty years from now.
As for PhDs - in my own area of interest the tenured people are pretty mediocre (believe me - I've worked through their papers) and most of the innovation and invention happens in industry.
So, there's no obvious benefit to spending the money. As it happens I earn enough to do research part time - no special resources needed in this field - and I'm getting a lot of satisfaction from making my own way for my own reasons.
Given these, I don't see why an organization can't get together and simply agree to communicate, work together, somehow find a way to minimally provide access to journals for its members and dutifully train new students and grant them degrees. A Phd may or may not be optimal, perhaps something less stringent. A lot of people I know personally didn't get in to the field because they wanted to get rich, some sacrifice may be required but at least there is no denying a sort of "volunteerism" in mathematics.