If match participation is dropping, then it's time to think about options.
The easy way to decide if lower round count matches are desirable is let the competitors decide.
Those who want a full round count match can do it that way.
And those who want a lower one can run it their way.
Everyone is happy.
This approach shouldn't be a hassle for local matches.
Higher level ones will always run under the rule book, and anyone going to one wouldn't want changes, anyway.
Lock the doors, they're coming in the windows.