Switch isn't something that can be copied on a whim and Nintendo knew that. I think Nintendo kept it close to their chest because that ensured that competitors couldn't come up with a coherent smear campaign to deride Switch while at the same time it would be much easier to maintain buzz from reveal to launch.
As for Sony turning the PS5 into a hybrid instead of going with a stationary home console, that's not going to happen. Sony is an America-first console manufacturer, so Xbox remains a serious threat despite a large gap in worldwide sales. The PS4 is only a few millions ahead of the Xbox One in the USA, the most important market. A hybrid PS5 couldn't keep up with the next iteration of Xbox and Sony certainly won't cede the AAA third party market to Microsoft. Sony isn't in a position with the PS4 that allows them to take the US market for granted.
If Sony decides to take on Switch, it will be a solution separate from the PS5, such as a portable PS4 hardware that can play PS4 ports natively and streams PS5 software from servers. Even that is a longshot though, because a separate device makes things more complicated for Sony and at its core it already can't compete with the convenience of Switch, let alone its game library. It's more likely that Sony's reaction to Switch will be the same as to the Japanese market as a whole, so basically leave it as it is while shifting their focus to greener pastures for themselves.
I hope so.
I want my Playstation 5 as a big black ventilating powerful box under my TV, as usual.
God bless You.
When PS4 will hit 100m consoles sold: Before Christmas 2019
There were three ravens sat on a tree / They were as blacke as they might be / The one of them said to his mate, Where shall we our breakfast take?