Thesis: The current concept declaration syntax does not conform to other syntax elements in the language and the write-how-it-can-be-used style seems rather alien.
Please follow Nim GitHub Issue 5770 that I opened in order to discuss strengths and weaknesses of the concept syntax and to discuss other suggested alternatives.
From the discussion we had on IRC we concluded that there is need to at least talk about and consider alternate solutions to today's concept syntax.
Additional proposals, ideas and arguments are of course welcome as always! :)