Thanks for taking the time to read, vote, and leave comments on my proposal for Proposed_features/Mimics. I'm not a grammarian but the vast number of keys are nouns and, as you say, the singular form is most suitable unless the value is expected to be plural, such as building:levels=*.
mimic here is used as a verb and my proposal reflects the way it would be used in a sentence, e.g., This cellphone mast mimics a cactus. Happy to discuss but I hope you'll reconsider your abstention. Thanks. –Erictheise (talk) 19:36, 10 December 2019 (UTC)