kimchisoup

sigh Yes.

because it's a secret and you don't want competitors to get advantage

Talk to your customers about their problems and their needs, not the solution itself. The solution can remain a secret.

because customers won't get the idea without a mvp

Again, figure out the customers problems first.

because revealing your idea might reduce your impulse

Don't reveal it until it's ready to be revealed.

because customers will ask for all kind of features and change your idea into something else, more practical, like "get a job" instead of dreaming in your great idea

If customers are asking for features, then there's your demand right there. Strategise on how you want to address it.