I dont want to say an opinion in general but i will throw my experience with S&C challenges.
While i am not a sculptor i love converting existing units and always have 10-20 projects in mind but almost every time i am holding off my ideas for a challenge to begin and put them in (nothing wrong with waiting a week or two) but every time the theme of the challenge never matches what i was prepared for (could be bad luck).Also sometimes the theme is wayyy to difficult to complete for conversions only (for example monsters or BOFTA, someone that does conversions dont want to alter his newly purchased high quality models
) but that could be the dream challenge for a sculptor.To conclude i too suggest more open themes where everyone could take part regardless what army he is currently on. For example instead of ''Mordor'' or ''kingdoms of men'' choose ''commanders'' or ''cavalry'' or ''new units to existing armies'', challenges that everyone take part regardless of the army he is working on.
P.S By all means excuse my english and absolutely this is NOT criticism nor any offense. Simply my personal idea because i love all those challenges and have helped me do things i thought i couldnt
