Actually, it makes kinda sense to use your phone as a secondary screen. ie. For DS virtual console or for game ports like Tokyo Mirage (let me dream at least) or some nifty functions like OP's example of Splatoon.
Luma has his own Splashscreen option before redirecting to a payload; https://github.com/AuroraWright/Luma3DS/wiki/Other-features-and-notes just be sure that you are using an updated version, also you can get some pre-made splashscreens @ Satchi's Magikarp thread here...
i dont usually post too much (i guess i've only posted once or twice since i joined) but i was messing around, making my own splash screens and i thought maybe some of you guys might like them.
they're all in the same zip with their previews btw