Google is now ready to move on to the latest draft version of SPDY, the third version, and has started testing support for it in Chrome. About 10 percent of Chrome users will have SPDY/3 support enabled in their browser. Google servers have started supporting both the current SPDY/2 and the new SPDY/3 last month.
The plan is to drop support for SPDY/2 as soon as the new implementation is considered stable enough. If things go as planned, that should be Chrome 22 or the next version after that.
SPDY is currently being considered as the basis of the upcoming HTTP 2.0 standard, or at least a portion of it. There's a long way to go before the Internet Engineering Task Force (IETF) even settles on what HTTP 2.0 should be like, let alone publish the final specs.
But work continues on improving SPDY as it is. The third draft version of the specification comes with several changes over the previous version and some improvements.
The differences aren't great, it's an evolution of the previous document obviously, so implementing them in the client shouldn't be too hard. With Google's servers already running SPDY/3, the clients, aka the browsers, have to keep up.
Given that only Chrome and Firefox support SPDY at the moment, this shouldn't be much of a problem.
The transition has already begun with Chrome 19 supporting the latest draft spec. At this point, 10 percent of users are already running SPDY/3 instead of SPDY/2, not that most of them would even notice. Mozilla is said to be working on implementing the new draft version in Firefox.
This will be an ongoing process though since, as soon as SPDY draft 3 is done, work will start on draft 4 and beyond, until the specs reach standard-candidate status.