Italy seems very close with only Dauphine and TdS missing but I dont see them winning these races the upcoming years. First of all I dont see any italian rider right now that would be able to win of these races but even if there would still be the problem with the Giro d'Italia before which would mostly be the target for Italians.
Spain is missing the cobbles classics which I dont see them winning the upcoming years. Same problem for Colombia.
Australia is missing so different styles of races that they would need some great riders. Ronde, Lombardia, Vuelta and Itzulia have very different profiles.
The UK is a bit behind right now but have surely chances to win some of the missing races in the next years. Ronde, Roubaix, LBL, Lombardia and Itzulia... Well, I would be surprised if Pidcock doesnt win at least one of these races. Maybe someone like one of the Yates-brothers has a shot at some races too and there is also Jake Stewart who I wouldnt underestimate for the cobbles. And last but not least some riders like Onley, Fred Wright and others who can develop to someone who has a shot at.
It's crazy that a small country with not that much cycling history like Slovenia has already won 11 races out of 17 while Roglic and Mohoric have a few years left and Pogacar looks like he just has started his career. Paris-Roubaix seems like the biggest issue to win right now.
Most surprising for me is that France has just won 4 of 17 races. We all know that they didnt have their greatest generations the last decades but it always felt like they had great riders who could win one or the other races, especially as they had riders for all types of races.