What really needs to happen is an open decentralized protocol needs to be agreed upon for newsfeeds + blog posts (wordpress) + microblog (twitter). Then everyone can write their own servers and clients and operate in a manner like Email currently works.
Then do it. Make everyone look like idiots for not doing it sooner. Make it so cool I have to sign up.
As a developer, I never thought once about building an app or integration for Diaspora.
That's why App.Net might have a chance -- he's making this about targeting developers. There's a reason Apple has spent millions marketing different 3rd party apps -- and the whole ecosystem via "there's an app for that". There's a reason "killer app" is part of our lexicon. There's a reason Steve Ballmer jumped around on stage screaming 'Developers!' and there's a reason XCode is free now.
Building it is not a guarantee that they will come. But it is a prerequisite.
Are there really that many developers clamoring to build new apps on yet another closed, for-profit, centralized social network with no users? I sure don't. I'm already done with Twitter and Facebook apps, the centralized model is simply not the way forward and I can't be alone with this opinion.
Techcrunch posted an editorial a while back that I agree with:
http://techcrunch.com/2012/08/03/the-federated-web-should-be...
Honestly, Facebook has a lot of frontend code. I don't think Rails is a bad choice for that. My experience with large systems is that they're usually not homogenous. There's no reason they couldn't implement the Rest API components outside of Ruby if that was their biggest obstacle to success.
Though I'm not sure it is, because even though you've obviously given this issue some thought, you didn't really articulate who was put off by their use of Rails?
Edit: To avoid confusion, Snowflake as in https://github.com/twitter/snowflake, not "snowflake schema".