Thinking more about the low quality entries problem, I wonder how tech challenges handle them - https://www.hackerearth.com/challenges/hackathon/ ; because it doesn't seem to be filtered with automation like I previously thought.

Perhaps may be it's because the amount of work involved to submit an entry is itself a barrier? Then again it should be case with several other categories e.g. say Art and entries should submit a video of them painting (or) like you said grammar could be a great filter for anything involving content writing.