Nintendo announced physical 3DS and Wii U games will not be compatible for the Switch but digital games could end up being made compatible during the Switch's life.
http://www.gamespot.com/articles/nin.../1100-6444706/
Blizzard debunking rumors of them currently working on a Hearthstone port for the Switch after saying they only used the official Hearthstone Twitter account to make a meme joke based on recent a teaser image involving Mario and the NX announcement.
https://www.destructoid.com/no-heart...h-394781.phtml