It's @dcurtis "concept" and let him decide, no matter how ethically wrong his decision is, its his' anyway. Copying the concept and releasing it is definitely not the right way of showing your discontent with his decision of not releasing his work to public.

I have an app that is closed source (the kind of thing that you would expect to be opensource but i decided not to). If someone thought that it was better if it was open and copied the concept, UI/UX and released it, i would not be very happy. Community and open is all good and i am all for it but i intend to make a living out if it [my app] and won't be happy seeing it being released. I don't know how much of a work the platform really was but my app was alot of work. more than enough that i would enforce it's closed-source status.