Apparently (?), SIE filed a patent for a Switch-like device with detachable controllers in 2015

[potato_hamster]

Guys, you're late to the punch.

This is a patent for a dock to use the PSP with Playstation Move controllers from 2011.

https://www.destructoid.com/playstation-move-dock-for-psp-go-why--201886.phtml
https://www.engadget.com/2011/05/23/patent-points-at-playstation-move-compatible-psp-go-dock/

If Sony did actually go through with this idea, they didn't steal it from Nintendo.