I do hope this Nintendo Switch Smash Bros has Adventure Mode, the Chronicle, and other features that were in Brawl but were removed for the 4th game. Compared to Brawl, I've always felt that Super Smash Bros. 4 was incomplete and missing some features.
Correct me if I'm wrong, but I think every game up to Brawl has taken all of the features from the last game and revamped them and added new features. To my knowledge, I think Super Smash Bros. 4 was the first game to start removing features that were in previous games. One core feature was Adventure Mode. Another was the Chronicle, which I really like, for some reason. I never cared that much about Tourney Mode, Rotation Mode, and stickers, but it still would have been nice to have them. I also like Brawl's Classic Mode better than Super Smash Bros. 4's. Brawl's Classic Mode feels more "classic" than Super Smash Bros. 4's. Smash Run feels closest to Adventure Mode, but it's not the same. It's not perfect, either. I wish you could beat up opponents and steal their stat boosts and such in the first phase. (The second phase is the final battle.) Super Smash Bros. 4 also introduces some features that just seem unneeded and aren't good, such as Smash Tour and Trophy Rush.
Super Smash Bros. 4 also feels much more competitive than previous games, and I'm a casual gamer and don't like to be the best. You're penalized harshly for losing Super Smash Bros. 4's in Classic Mode, and, in Brawl, you can just get right back up and continue with no penalty.
I still like Super Smash Bros. Brawl the best. I just like how it's so casual. It doesn't have that competitive feel that Super Smash Bros. 4 has. And it has a HUGE Adventure Mode. Not to mention, the game has a HUGE modding community, and that REALLY keeps me playing Brawl. One thing I like doing is playing through the Subspace Emissary using modded characters.
TLDR: Super Smash Bros. 4 feels incomplete. If this Super Smash Bros. game on Nintendo Switch adds back features like Adventure Mode and completes the incomplete Super Smash Bros. 4, then maybe I'll be happy and not be mad at Nintendo for ripping me off if it's a port.