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:
That said, there's already a working Twitter-like distributed network. I hard my own StatusNet node running on my personal server and getting messages from people on Identi.ca, until I realized that I found the idea of the platform interesting, but not the platform itself (nor Twitter, for that matter). The fact that half the accounts were abandoned didn't help either.
StatusNet actually sounds kinda good. Why isn't it more popular? I'm not sure, perhaps people need something more than just a replacement for Twitter. I think something that will eventually become successful will be some sort of multi-use low-level protocol that handles many types of "social communications", for example: Twitter + WordPress + Private IM + Voice Message.
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".