Interesting idea! But...
Matsutake gohan is to enjoy the flavour of matsutake.
If you use it for omuraisu, the smell of omlette might kill the flavour (or crash against each other) - perhaps it is just a question of taste, but if I'd use kinoko (mushroom) for omuraisu, I'd rather use something like maitake, which has stronger in taste tha in flavour... you can add more kinoko, such as shiitake, shimeji, as well. And definitely "NO KETCHUP".