Set up a very short timeframe and goal - let´s say, I´m going to make a prototype (or code feature X) this weekend.

Then show it here :) .

The risk of it "getting stolen" exists, of course.. but if you don´t do it it´s exactly the same. If you aren´t convinced, you think someone else will have the time and commitment to do it? Unless they were already planning on it.

My recommendation: go ahead and do it. Maybe you need some structured help, join a hackathon?