I read this somewhere, maybe Reddit, and it's quite an intriguing theory.
In Breaking Bad, Walt has a habit of taking on some little traits of the people he has killed.
When Walt killed Crazy 8, he started cutting off the crusts of his sandwiches — just as Crazy 8 had done.
Gus drives a Volvo. After Walt kills Gus, at the beginning of Season 5 (at the Denny's), Walt is driving a Volvo (w/ NH plates).
When Mike and Walt meet at a bar in an earlier season, Walt orders his drink neat while Mike has his on the rocks. After Mike is killed, and Hank offers Walt a drink in his office — he asks for it on the rocks.
At that same scene at Denny's, Walt arranges his bacon into his new age. Someone else used to do that. On top of that, he's using Skyler's maiden name on his fake ID.
Based on his history of picking up traits from his victims — I believe Walt is going to murder Skyler before the series is over, and it probably had already happened before he showed up at the Denny's in the Season 5 cold open.