Well, if you're strictly talking about playback to a device that only supports one sample rate (which was not clear in your original post) then it could be even simpler:
Just resample it and play it. There is no other option for playback, other than non-playback. It will be reported in audio path. On devices that truly only support one sample rate, what is there for MC to discuss or negotiate with the user? tij mentions that they could chose another sample rate if MC guesses wrong, but not really, because there is only one choice.
It seems to me the complication only comes in if someone is changing the hardware playback device in the current zone. The DSP output format persists with the zone, not the device, so making persistent changes to Output Format screws up your playback if you change the hardware device again.
I wonder if it might be better, or possible, that if the user does go and selects a different playback device in the current zone, MC throws a dialog that asks "You're changing your output device. Would you like to create a new Zone for this new device, using the current zone settings?" If they say yes, it basically clones the Zone, and then any subsequent output format changes will be confined to the zone for the device.
Isn't it the switching of output devices that causes the issue? Someone who only has one device, and that device only has one sample rate, has no choices to make. It's multiple devices, or devices with multiple sample rates, that have choices that need to be preserved.