I will answer all your questions but can you explain bit more what do you mean with your base question, "Have you developed an application for a consortium of equal member" ?
Sure. I think of the different approaches how non-public blockchain projects are being started and managed. R3 and IBM (for example) start a lot of projects with their customers, but keep the leadership, so they have a traditional project structure with central councils that make the decisions.
This is in contrast to the distributed technological nature of blockchains, where every participant has equal rights. Of course we see developers forming groups as well as miners forming pools, so not every aspect of public blockchains shows a pure form of equality. But we also see (the return of) DAOs with democratic structures implemented in their own code, so that the governance of a blockchain project can resemble the structure of the blockchain.
Back to my question: Have you seen companies forming a consortium in order to develop a blockchain based system with democratic governance / without having a leading company?
Oh I see, well asked, brilliant question.
I think 2 things will happen, and several other sub versions.
Companies, especially the big, already established one are/will be forming alliances and use blockchain not for its decentralization but for the "shared immutable state", so they don't have to trust themselves and have a perfect audit system. I think of blockchain as a complicated MySQL replication where you can't delete or update rows. That's it. And this can be very useful in many scenarios with a leading centralized company in front.
New companies, projects will/and do use blockchain and the form of a "decentralized governance" as a pitch, looking for an edge, an opportunity on a market. I call them experimental bunnies. Like DAO organizations. What I like about this style, is mainly the concept of "delegated vote" or the approach of "weighted vote". In BI departments, business intelligence working with data, the concept of assigning a "weight", "importance" to something is really interesting. I would love to see whole countries actually having democracy based on staking or weighted votes because 1 vote of a doctor shouldn't equal to 1 vote of an engineer or any other profession in different contexts. People shouldn't vote for things they don't understand IMO. That's why I don't argue about politics, neither with my doctor. I argue with my dev colleagues haha. And if this would be successfully implemented, Americans wouldn't have this shitty president.
I think both approaches are valid and there won't be 1 good silver bullet.
Also, back to your question, I don't know a company who did it successfully yet, BUT my company will have it's own PoA production blockchain next year (for now is a test-network), and at the beginning we will make it more "centralized on decisions" to speed up the development and updates but also enough decentralized to keep users and data safe by having alliances with other companies and public communities so they still are the custodians of their data.
Funny enough, final goal would be to find a way how to "check mate?" ourselves out of the equation and that's the complicated part. It basically means, if you do your job properly, in a decentralized manner, you end up being obsolete but that's how it should be. So I think companies will follow such a path only if they find another area producing enough revenue to keep innovating and producing value for users. If that makes sense.
Let's stay in touch we can discuss this more as time progresses! Add me on LI.
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