all useful grammatical features that are available

Is there a chance to agree on which gramatical features are useful?

For example, what colors does the language have words for? Does it distinguish gramatical singular and plural? How about dual? How many tenses? Clusivity? Honorifics? Etc.

My intuition is that in a "perfect" language all these things should exist, and all should be optional. (Not sure about the colors; perhaps we should have separate words for "green" and "blue", but also one for "green or blue", and also one for "light blue" and one for "dark blue" to make everyone happy. I hope the list would not grow too much.)