I hope they put out a demo for it so I can try it out first, otherwise I'll probably just be on the lookout for a sale at some point. I was pretty disappointed in NSMBU:D even though I normally love 2D Mario games. I guess that's what makes me wary of 3D World in that its more like a 2D Mario in 3D, and the last 2D Mario was pretty mediocre and the only game on Switch that I have that I felt wasn't worth the money.
Nintendo loves 3D Mario. The previous generation was when Nintendo did everything they could to make 3D Mario sell better than 2D Mario, hence why all the cool ideas were reserved for the 3D games while the 2D games were treated to the bare minimum. The staleness of NSMB2 and NSMBU was intended.
Also worth mentioning is that we are close to completing year 8 without a new 2D Mario game and that despite how appropriate it would have been to celebrate 35 years of Super Mario Bros. with a new 2D game.