Recently Nintendo released Version 5.5.2 U for the Nintendo Wii U. While there aren’t any noticeable differences, data miners have found this line of text: “The Miiverse service has ended. Miiverse and any software features that make use of Miiverse are now unavailable.”
This could mean that Nintendo is preparing to close Miiverse on the Wii U soon. It is still unknown what will happen to Miiverse on the 3DS as the 3DS is still being supported.