Universal Nintendo': Switch 2 will feature physical and digital backwards capability, devs have access to enhance Switch 1 games Rumor - Nintendo, Page 2
For the record, NateDrake and John Linnenman from Digital Foundry had mentioned that BC is likely to be a bit more vanilla than this write-up suggests, in that it's not going to natively do anything for games that go past their current bounds, so games that are virtually flawless already like
Everything You Need to Know About the Nintendo Switch, So Far - Feature
Learning From The Switch: How Should Nintendo Launch Its Next Console? : r/NintendoSwitch
Nintendo Wii U review
Nintendo Switch 2 Backward Compatibility Functionality Is Allegedly Being Tested By Developers : r/nintendo
Nintendo – Working Casual
Nintendo DS - Wikipedia
So, Where Does Switch Fit Into Sony And Microsoft's Next Gen Landscape? - Talking Point
Nintendo offers vague answers on backward compatibility for “Switch 2”
Nintendo Needs the Switch 2, Not a New Gimmick
Universal Nintendo': Switch 2 will feature physical and digital backwards capability, devs have access to enhance Switch 1 games Rumor - Nintendo, Page 7
Nintendo Announces Switch 2 and It's only Backwards-Compatible with GameCube Discs, by Dunko Xyvir