I think this where some bureaucracy would be in order. Have a list of rules somewhere for the project. Have a list of close reasons based on the rules. One of t

I think this where some bureaucracy would be in order. Have a list of rules somewhere for the project. Have a list of close reasons based on the rules. One of them will be "Feature Request Declined". With the rule being "If you ask for a feature, we will consider it but we cannot guarantee to implement it, we may close it with Feature Request Declined because of time constraints, priorities or just that the maintainers need a life outside of doing this.". This might take the emotion out of it.