The Lord Commander of the Kingsguard is in King's Landing, but is not present at the king's wedding? That makes no sense.
Not only is Last Hearth correct and it impacts Jaime and Tyrion's relationship, but there's a rather significant plot point about Jaime belittling his fellow Kingsguard members for letting Joffrey die. If Jaime is present and the king dies, then he's equally to blame. Maybe they'll cut that angle out completely, but I think it'd be a shame because it establishes his authority as Lord Commander, and his relationship with the other Kingsguards, quite strongly.
So as Last Hearth said, an important aspect of Jaime not being around is that Tyrion has no witnesses to stand for him at his trial. Jaime would never testify against Tyrion and would even testify in his favour. I just don't see how they could write this without it being all wrong and awkward. I just don't like it.
Eh. Maybe he will testify in favour of Tyrion and that's what will drive a wedge between Jaime and Cersei, instead of them just discussing that in the White Tower? I don't like it much, but I can't think of anything better at the moment. That said there's the issue of Jaime refusing Tywin's desire to leave the Kinsguard and become his heir, too.
I'd prefer if we didn't see Jaime (or if they used the sitting-around-a-campfire route à la Bran/Osha xD) for a few episodes, than mangle this story too much. Maybe they'll find a clever solution, but I can't think of one that I like right now.