Wouldn't it just be something similar to the way you record your gameplay onto your PC with a capture card? The only difference would be that instead of saving it, it would just display it.
My DS upper screen is messed up, and I wanted to see what was going on without having to hold it in a...
btw i feel this a good time to remind you guys that sea of thieves was made by rare, who also made DKC1-3 and DK64, alongside banjo kazooie and conker's bad fur day