Has Harald ever spoken in public about a possible abdication? We know that QMII has said that she doesn't indend to abdicate, but has Harald said the same?
I also think that Norway is in a special situation. They don't have a pool of working royals, or royals at all. Compare to Sweden. Even if CG is in reasonable health, I think that Victoria would be more than ready in a couple of years (when the kids are a bit older). She has support from her siblings - Madeleine is moving back to Sweden this summer - who can do occasional jobs until her own kids are old enough, and is very popular herself.
But in Norway, Mette-Marits health isn't good. Märtha is... out with the shaman on adventures. Ingrid Alexandra seems to be a very capable and smart heir, but she's also very young. So I personally think that Harald is hanging in there as king because he knows that Haakon will have to carry a heavy workload when he becomes king.