Its an interesting proposition, but fundamentally broken. Lets say you build it (and frankly I think a better course here would have been something based on the app.net model rather than WP Engine model) and its "successful" what does that mean to you?

Here is the challenge, there are too many scenarios where you don't want to be.

#1) "SPLOGGING" or some random thing becomes the new thing which all the cool kids are doing. You've got just enough customers to keep you in Ramen so you're committed to working until you're 70 and can augment your income with Social Security to honor this commitment to those few.

#2) You've spent 20 years maintaining the service, answering the same questions, fighting the same fires, dealing with the same sort of "Chrome v286 can't display tri-graphs properly without mime support from the replacement for nginx" kinds of problems.

#3) Its wildly successful and someone offers to make you a billionaire if you sell it to them?

In contrast I like the foundation idea. Foundations don't get tired, they don't get tempted, they just execute against their created principals. A foundation with an endowment that runs a service which supplies a voice for bloggers for a computed value which is not to exceed 15% of the operating cost of the service. That is a durable kind of construction, the people in it are just employees, they turn over like students in a college or wait staff at a restaurant. Its a chunk of money, controlled by a legal document, implemented by a management structure, to create a service in perpetuity.

Don't build a business and promise not to sell it, build an institution that is self contained.