I think "MW" is a great song to end this monumental year with!
And traditionally, Johnny's has their own countdown that kind of runs at the same time as Kouhaku (which I think SMAP aged out of). I think because of the different units, it'd be hard to cooperate, so they just leave them out all together. ALTHOUGH, I'm sure if just one year they include Johnny's, and Johnny's Jimusho actually agrees, the viewership of Kouhaku would just SKYROCKET to like, at least 60%.