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With a Switch 2 looming, Nintendo is sending out the original with a bang
(www.theverge.com)
This is a most excellent place for technology news and articles.
Gameboy Color was backwards compatible with Gameboy cartridges. Gameboy Advance could play Gameboy Color games. The DS was backwards compatible with Gameboy Advance. The 3DS could play DS games.
Wii was backwards compatible with GameCube discs. And Wii U was backwards compatible with the Wii discs. The switch form factor didn't make sense to be backwards compatible with Wii U, and also Wii U was a commercial failure and didn't sell well, so less people who would be buying a Switch probably didn't have a Wii U.
I think that if Nintendo has a successful platform, they do try to have the games released on the platform last for about 10 years, so Switch games should hopefully be playable on whatever Nintendo's current console is in 2027 (10 years after switch launch)