If you are making a client for anyone besides yourself at some point people will expect to be able to use one of the many "optional" features. At that point it doesn't matter if you technically don't need to support it as users will then simply see it as a shortcoming of your client.
So if we are talking about anything more than a MVP client these optional specs should be included in the argument as only being optional in theory.
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With all due respect but
If you are making a client for anyone besides yourself at some point people will expect to be able to use one of the many "optional" features. At that point it doesn't matter if you technically don't need to support it as users will then simply see it as a shortcoming of your client.
So if we are talking about anything more than a MVP client these optional specs should be included in the argument as only being optional in theory.