It was Halo and when the tease happened there was 100% backing to such a project being shopped around and planned. Considering the silence, odds favor the project being shelved for any number of reasons.
Because we'll never know, let's invent a wildly untrue story to run with and act as if it's real. Here's my candidate:
Phil Spencer was 100% into the idea of bringing Halo to Switch because he's a giant Smash fan, and his hope was that Master Chief having a game on Switch would boost his chances of being added to Smash Ultimate. When Doug Bowser told him that the final Smash character was Sora and not Master Chief, Phil Spencer went into a wild, blind rage and pulled all funding for Nintendo based products.
I mean here's my genuine take: Maybe trying to port a Halo game to Switch was proving entirely unsuccessful, so one of two things happened: MS decided to wait for more powerful hardware from Nintendo, or more likely IMO, they're going to leverage their cloud gaming tech to bring Halo to the platform in a cloud streaming way. I've actually thought about this a bit, and while I don't think there will ever be a simple "Xbox Cloud Gaming" app on Switch, I don't think it's entirely out of the question for MS to create individual streaming apps for each first party Xbox game (and maybe even third party games?) they want to bring to Switch that you can buy for $60 OR you can sign into your Xbox account (w/ Game Pass Ultimate) and play without paying anything extra. This way they can't eat into Nintendo's digital sales numbers by not offering games Nintendo is selling, while still leveraging that audience to boost their Game Pass subscriber numbers. Win win all around, tbh.
But the "no Chief in Smash" story is more fun.
Their new "BLONK" sound sucks! They should bring back "SEHHHHHH GUHHHHH"
Actually they should do the Puyo Puyo Tetris thing and record the voice actors for the main characters saying "SEHHHHHH GUHHHHH" and randomize which character says it every time you boot the game.
So yeah FEH is uhhhh not for me. Maybe if I was more familiar with the stories or characters but as it is I don't feel it's worth delving into all of the many many mechanics and modes, none of which are tutorialized well.
FEH more like FOH am I right