My opinions have very steadily changed on Smash for Switch. Originally, I was very adamant that the title would be an enhance Smash 4 port, with maybe about 60% Wii U content, 20% 3DS content, and 20% new content.
Link having a new costume does not make me think it's a new game, nor does any part of the reveal trailer. However, things such as the game not being stated to be a port, and the wait time between Smash 4's development and this game has me thinking this will be a new Smash 5.
However, I still think it will heavily take from the Wii U game, including models, possibly physics and mechanics, stages, etc. Basically, I do believe it is a Smash 5, but I believe it will be maybe 40-50% Wii U content still.