Well, some effort needs to go into some plugins for nginx and varnish. nginx needs to route incoming requests to the right varnish, and some custom cache invalidation stuff should happen on varnish as well.

Other than that? Lots and lots of python, of course ;) I'm only one guy, and there are three or four big moving parts that need to be written. Something to build eggs and push them, something to monitor and manage processes on individual servers, something to dispatch requests to the appropriate servers, and something to monitor and manage the database servers.

Even pulling back and looking at a minimum viable product, I'm still doing most of that work, just far simpler versions. Succinctly, it's too big for me to tackle on my own in the next six months.