SEGA has been running a somewhat chaotic live stream for its 25th Anniversary Sonic bash (at the time of writing), with delays and atrocious sound being issues early on. The disappointment continued for Nintendo fans when a new Sonic game was announced without any mention of Nintendo platforms.
Sonic Mania is a remix title, in some respects, blending re-imagined classic stages with new zones and gameplay twists. Sonic, Tails and Knuckles will all be playable, with this retro-style 2D entry being a collaboration between SEGA, Christian Whitehead, Headcannon, and PagodaWest Games. The trailer only lists it for PS4, Xbox One and PC.
It's not impossible that the NX could get the title and simply be announced after the hardware has been revealed, but that's only wishful thinking at this stage.