The Game Boy-Game Boy Color wasn't really a planned thing by Nintendo, when people cite that they need to know what they're talking about. Game Boy sales had collapsed by 1995-96 (from a peak of about 16 mill/year down to about 5 mill/year).
Nintendo was working on a 32-bit Game Boy successor codenamed Atlantis at the time. It was supposed to actually be far more powerful than the GBA, it was even supposed to display 3D graphics, I'd guess probably like maybe a Sega 32X range system.
The system had development problems and never came out. So they rushed Virtual Boy to the market because Yamauchi wanted at least something to help make up for declined Game Boy sales. That flopped.
Then something completely unprecedented happened, Pokemon, which no one expected to be a hit, took off in Japan and Game Boy sales started to rise again there. To capitalize on this Nintendo slapped together a Game Boy Color model as Pokemon took off worldwide. GBC could run exclusive, specific games and was kind of like its own platform.
The rest of Nintendo's system transitions have been fairly straight forward, 5-6 year primary product cycle, a couple of revisions maybe.
What I could see is a more phased transition with more cross-platform games. For example if Switch 2 comes out in 2023 and there's a 2D Mario game, there's no real reason it couldn't run on Switch 1 and Switch 2, and just run on Switch 2 at 1080p portable/4K docked. There's lots of Nintendo franchises quite frankly that could be like that.
