Most of SO's operations are something I would not like to fund. I'd be happy to donate for their core service, but that's really only 10% or less of their headcount. Who funds the other 90% and why would they want to?

SO is too big to go for a Wikipedia style model unless they strip off just the core SO part and relevant engineers and make only that part donation based. And I'd guess the other 90% would end up in layoffs anyway.