You can only future proof your game so long as the future is paying attention.
UPDATEAs of a patch on 2/21/2024 this issue has been resolved on Nintendo Switch.
UPDATEWith Jet Force Gemini now available in other regions, we've produced a more in depth video explaining the issues outlined in this article.
Jet Force Gemini is available on Nintendo Switch right now via the Japanese NSO app (the new 18+ one). However this release does have a very obvious bug that's a huge disappointment, especially in handheld mode. Jet Force Gemini was one of several Rare games of the era to support a 16:9 widescreen aspect ratio. Goldeneye 007 offered this same feature, and the Switch release took advantage of this, making it the default display mode.
In Jet Force Gemini however, turning on widescreen mode does not properly scale the image.
The 4:3 border does disappear, but the image is letterboxed rather than being properly stretched vertically to fill the screen. When playing docked you could conceivably adjust your picture settings to manually scale the image, but when playing handheld there is no way to display the image correctly. Below I've manually rescaled the image to show how it should display on the Switch screen.
Perhaps by the time this game makes it to the North American version of the NSO service, this bug will be resolved. For now I'd stick with 4:3 mode if you're playing the Japanese version.