Good suggestion!
I generally think it’s fine to post “inappropriate” solutions if there’s a tangible advantage to them. It would be silly I think to not even mention a possible 2x speedup because it uses internals (as in this example of updating a dictionary). I often see newcomers here benchmark Julia code to another language and be disappointed if the performance isn’t the same.
BUT – I agree with you that it’d be a good idea to hold back unless there’s a clear advantage, and above all I think that we could be better at providing proper explanations/warnings for these cases, and not be shy to point this out when we see it in others’ posts.