Still way too speculative. Valve already releases their dedicated servers for linux. They might just be looking for someone else to help with this. It seems you have another source for the client being ported than just the job posting, but until I hear more about who or what this source is, I'm go to remain skeptical. Even if they are working on a linux port, there's no guarantee it will be finished. It's not like their business depends on porting the game to linux, so if the project runs into any bumps it'll be the first to be dumped.
Still, it would be nice if steam and the source engine was fully ported to linux. I'm just really skeptical that it'll happen.