A McKeon retirement has been speculated for months. McKeon gave a non-denial denial later in the day that he hadn't made a decision yet. I can't think of another district where not one, but two challengers are fundraising but will only run if the incumbent retires. Yeah, "if."
This District isn't winnable for Democrats. A lot has been made of Buck McKeon's 2012 55%-45% win over some dude Lee Rogers. The theory goes that if McKeon has a real opponent he might've lost. There's nothing to this. While a better candidate might've done better, McKeon is notorious for not campaigning and spending more time outside the district helping other Republicans. The McKeon family was far more concerned with helping Buck's wife Patricia win an assembly seat. Tony Strickland and Steve Knight are candidates who've been through tough elections and will put a lot more effort into an election than McKeon has.
McKeon's performance wasn't that bad. He finished 3.8% ahead of Mitt Romney. The average Republican in California competitive/semi-competitive seats finished 3.3% ahead of Romney. Darrell Issa was 4.8% ahead of Romney and Dana Rohrabacher was 5.0%. That's not that much better. This simply isn't a 60%-40% seat no matter who runs. But it's also not a 50%-50% seat either.
We also should keep in mind that 2014 will be a mid-term and every statewide Democratic candidate lost this district in 2010, even the ones who blew out their Republican opponent. Even Diane Feinstein couldn't win the district. This was an R+14 for Emken.
The Democrats don't have a candidate who can win here. Yes, I know I've said that about Riverside County and CA-41 but that was a district that Obama won by 26 points. If Obama is winning by that amount, Democrats can run anyone and still win. They can't do that in a district Obama lost.
Could it be competitive in 2016? I doubt it. The district went from R+3.4 in 2008 to R+2.9 in 2012 when so many other districts were making big moves toward the Democrats. The aforementioned CA-41 went from D+6.9 to D+10.9. So it seems unlikely to move to D+ territory it'd need to for it to be competitive. Democrats will again run "some dude," while the GOP will run a sitting congressman.