The Wifi Alliance may wish to provide guidance on this, at least for the residential space. Some ideas:
* have the router/AP do a speed test (at boot; regularly), and if the connect is ≤X Mbps then the wider channels won't help anything;
* do a sweep of the band (boot up; intervals), and if ≥Y% (50?) of it already in use, default to narrower channel.
Either/both of these would be done on a default "Auto-choose" setting, with allowable manual override.