Is Minecraft Coming to a Standstill?!

As you mentioned, players counter does go down when "update" getting older, content being a bit stale resulting non-interest for the game. In fact time to time, this happens almost to every game thus when Minecraft releases a new update it will attract back some of the community and gain back the popularity the same as Terraria. You got a point on Minecraft losing content which I think you have to speculate that Minecraft is an open world with massive potential yet to be discover, many ideas were tossed around about next update to be, what lore would be tale, and probably new mechanism would be implement. To my point of view minecraft is not being into a standstill, it still surrounded by big community (modding, server, etc) just to keep it going for now.