Seemingly yes. My most basic argument on that is that these components are commonly found in modern server stacks, so chances are that you are already using them, you know how to configure and setup. If I am already using Nginx & Redis and Sphinx as a full-text search engine, why not have something to facilitate the search in modern manner, almost out-of-the-box? As far as the clustering part you are referring, I don't have an exact scenario on my mind at the moment but I believe it can be done. Please keep in mind that this is the very first beta version and hopefully with several contributions, it will undergo many significant changes.
In order to handle realtime indexes Sphinx requires using SphinxQL which in turn uses MySQL client protocol. So you'll need the MySQL client package. MySQL server is not strictly required and I am guessing can be replaced by Postgres since Django models make the DB backend transparent to the developer.
