Kudos to Nintendoeverything for the translation of the recent Nintendo Dream Article.
The original game according to Hiroya Usuda was made for 1080p with 30 Frames Per Second, however its now revealed that a mode raising the FPS to 60 for the trade off of scaling down to 720p exists. This however only applies to the Switch version.
In laymans terms this pretty much means.
New 3DS owners should be able to at least handle 30FPS, however those without will likely want to either upgrade or get a Switch if they have an interest in the game.
Should be noted that Hyrule Warriors has no such option, this is also the first Switch game to my knowledge that has had such a feature as well.