It's probably a niche market, but most games on the switch run natively at somewhere between 720 and 1080p and look awful scaled up to 4k.
Native 720p does look slightly better than integer scaling to 2x because of subpixel stuff, and generally liking that LCD look. But integer scaling would be enough really.
Sounds like a fun project, you should build one.
Taking in a 720p hdmi signal and pixel doubling to 1440p or tripling to 4k and outputting that as a valid HDMI signal without adding more than a frame or two of lag would require custom chips. Although maybe a software solution involving a gpu might be possible?
Implementation is left an as exercise for the reader.
There must be TVs or scalers out there you can buy that are used by retro gamers and let you runt 1:1 scaling on modern TVs. Or you can emulate the Switch games and run them at natively higher res.
Either way, I'm sure there are solutions for you out there instead of display manufacturers having to go back 20 years in time to serve an outdated gaming console. Just a thought.