I noticed that there seem to be a lot of threads about how to keep people at cap. The answer is simple, we need a new raid that requires farming to be able to craft the gear (so folks are encouraged to run it over and over) and has high end stats. In fact, I'd argue the best way to make folks stay at the high end is to make ALL new raids have this kind of gear. The easiest way to make this happen currently would be to buff the stats of Legendary Shroud. Strahd and Baba (to the best of my understanding) do not require this, so other than people running it a few times because it's new and interesting, you get your couple of drops that you care about and you're done (and a few might keep farming for tomes) and that's it.
But if the raid required more farming than that *and* additionally allowed you to craft items for different slots like Shroud, then not only could everyone make use of it but there would be a much more long term need for the drops from the raid, people might even be encouraged to keep multiple characters at cap to get more drops faster.
Obviously the TR grind will still pull some people away from this - once that was introduced, there were always going to be less people at cap than a game like WoW that doesn't have a TR mechanic, for example. But this would create more of a reason to stay at cap than we have now.