Public Ideas — I have 15 losing contest designs and notes on why each lost. What could they become?

Love the fact you actually collected the feedback and learnt from the experience, well done! You must not be the only one who has a lot of "failed" designs, maybe it's worth some thought? A platform where people can choose from those and buy them cheap? Or maybe put them on fiver with fixed price? Or some crazy-er idea - can gamify it since you are a game developer - so designers can train their skills by looking at designs and either guess why those failed or apply fixes until the designs actually work?

Oh and also you can share your findings here and be part of a book!

One thing I'd love to see is what happened after you started winning. Could you take three of your early losing entries, redesign them using everything you've learned, and show the originals alongside the new versions? The comparison would probably teach more than a list of design rules. You could even ask other designers to critique both versions without revealing which came first.