Last night, on the eve of Xenoblade Chronicles 2's worldwide release, the game's official Twitter announced that KOS-MOS Re: will make an appearance as a Rare Blade.
Here is the character's introduction clip, which is in Japanese. (However, it does not state whether or not this is a Japan-only exclusive.)
— ゼノブレイド２ (@XenobladeJP) November 30, 2017
Android KOS-MOS appeared in the Xenosaga games, Monolith Soft's previous Xeno series.