I only picked Shannon because it's on the west coast -- I figure, if you're going to bike west to east, you might as well start all the way west.
Caretaker, I didn't mean that Georgia would be boring! -- I'd love to see Georgia/Armenia/Azerbaijan. It's the 1,100 km along the Black Sea to get there that sounds a bit monotonous. I've already spent quite a bit of time in Turkey, so that's rather lower priority than other areas.
Axolotl (great name) -- thanks for the pointers on France. My routes were just ideas, starting from the thought that I'd love to ride Ireland but I don't want to miss Spain. The areas you name sound great. Not sure how to work in Spain, France, and Italy, without swinging all over Europe, so I may need to cut some out. But I have lots of time, so that's not the problem.
I was actually just driving in Normandy last month, and the roads were among the narrowest I've ever seen -- they would have been simply terrifying to bike on, with barely enough room for two cars to pass, and no shoulder at all. I had a similar problem in Scotland, where the shoulders were nonexistent by American standards; and in many places there just weren't "back roads" in the sense of being little used. It was often stressful. I'd like to find good back roads for relatively safe riding, at least better than those I saw in Normandy...
Croatia sounds great, and in fact much of the eastern Adriatic looks pretty good. I'm interested in Albania too. Other suggestions of favorite rides for East/Central Europe?