I'm not sure how I feel about the chances of a DK newcomer. The timing of all this is just terrible.
First, we have the Wii U Tropical Freeze, which came out in early 2014. It was way too late to receive a character in Smash 4, and the most it got recognized with was a few trophies.
Then the development of Smash Switch began in 2016. At the time, Tropical Freeze was almost non-existent. It became a highly forgettable Wii U game, and both Nintendo and its fans rarely acknowledged it. Needless to say, I don't think DK was at the top of Sakurai's head when he considered newcomers for this game.
Finally, we have the Tropical Freeze port, which just like its predecessor, had awful timing for Smash. Once again, it looks like this game came out way too late for it to receive a character in Smash.
I'm not saying it's impossible, because unexpected things do happen from time to time. However, based on these patterns, I'm not holding my breath for a DK newcomer. I hope I end up being wrong though.