While Nintendo won't come out and actually say it, the 3DS is pretty dead now. All of the major publishers and developers have shifted their attention to the Switch, and as a result, the older handheld system has seen its list of releases dry up completely. 2019 is looking pretty barren for 3DS owners as far as new releases are concerned.
However, a game announced during a Japanese Nintendo Direct in 2018 was supposed to be on the horizon. Mixi's Mobile Ball was shaping up to be a rather unique action / sports title that would feature cross-play with a smartphone edition.
Sadly, the company has now confirmed that the game has been cancelled due to it not reaching the quality level required for release.
Here are some scans from Famitsu, posted in October of last year (Thanks, Nintendo Everything):
Despite its popularity in Japan, where it sold fantastically well, the 3DS is now seen as old news by players who have fully embraced the hybrid Switch. The cancellation of Mobile Ball could well mark the true end of the 3DS' lifespan.