Super Smash Bros. for Wii U apparently alluded to Super Smash Bros. Ultimate several years ago

It looks like the recently-announced Super Smash Bros. Ultimate may have been teased several years ago via Super Smash Bros. for Wii U. This stems from an in-game mission called The Ultimate Battle, which is attached to the following description:

They’re all here! Every single fighter! If this battle’s not “ultimate”, then what is?

As you may have already heard, Super Smash Bros. Ultimate will include every single fighter from the series, pointing toward the possibility that director Masahiro Sakurai was already thinking of the next game.

In Japanese the event is called, "究極決戦" which translates to "The Ultimate Battle" in English.

Since Smash Bros. Ultimate is called Smash Bros. Special in Japanese, it might be an unintentional pun.
(Thanks to @JV_Jardim for tagging us) https://t.co/gTmQmcqZGW

— Source Gaming (@AllSourceGaming) June 23, 2018