During the Pokken Tournament World Championship, it was announced that soon will be published a demo of Pokken Tournament DX Nintendo eShop to Switch, as you can read from the message disclosed on Twitter.
Can’t wait for #PokkenTournamentDX? Keep an eye out for a downloadable demo coming soon to Nintendo eShop! pic.twitter.com/awKkPIS21E — Pokemon (@ Pokemon) 20 August 2017

Note that the output of Pokken Tournament DX is waiting for the next22 September.
You can find all the news and articles about the product in our card.

Source: Nintendo Everything