Juan Carlos: my dodgy past is rapidly catching up with me and I am out of here while I still can.
IMO there won't be another abdication for another 10 years at least. That's the absolute soonest I could see Henri deciding to hand things over. All the other monarchs from countries that don't have a history of abdication (Liz, Marg, Harald, CG, H-A, Albert
) will be in it until the end, I think.
Albert really waited much too long to start a family. For the sake of the twins I hope he has a long and healthy life/reign like QE2. Don't think abdiacation will ever be an option for him.
I also doubt there will be abdications in Denmark or Norway. Regency is a real option if there are health problems but I don't see MII and Harald abdicating, it seems to go against their concept of monarchy..