Since Google servers and Chrome already support it, the chicken-egg problem might be solved. Firefox has an incentive to implement it to make Google search faster and other web service should implement this to provide a smoother user experience.
Yes. And just to argument this, here is the relevant except of the FAQ:
Q: Is SPDY a replacement for HTTP?
A: No. SPDY replaces some parts of HTTP, but mostly augments it. At the highest level of the application layer, the request-response protocol remains the same. SPDY still uses HTTP methods, headers, and other semantics. But SPDY overrides other parts of the protocol, such as connection management and data transfer formats.
Since Google servers and Chrome already support it, the chicken-egg problem might be solved. Firefox has an incentive to implement it to make Google search faster and other web service should implement this to provide a smoother user experience.