When I started playing the violin twenty something years ago my teacher put 2 coloured dots on the finger board, one where my first finger should go and one where my third finger should go. I seem to remember that I only had these dots for about 3 or 4 months....not long in the overall scheme of things. This worked because I could feel the dots, I didn't have to be able to see them.

I can't see how a fretted fiddle would work. Would it not be detrimental to the learner to have frets and then for them to be taken away?