I don't know, but I've seen some streaked mouse hostas with quite a lot of white on them. Calico Mouse Ears is on the hosta library auction right now, and some of those leaves are very yellow.

But is yours sporting into yellow or white? Because yellow may have enough chlorophyll to support the plant, whereas white generally adds no energy to the plant. Yellow has a decent chance of survival.

Let's see a pic!

Last year I bought a Mighty Mouse just for the all gold plant that was in it. I was too anxious and separated it from mama and it died. The guy I bought it from did not think there was an all gold mouse at that time.
So be patient and good luck!
Look forward to pics!

Melissa, doing a quick check of all the various sports of BME there does not appear to be an all-yellow sport. Nice find! I'd be inclined to grow this on for a couple of years just make sure it doesn't fall back into a variegated, the other thing I'd be concerned about is going from the yellow it is right now into a white, seeing as 'Mighty Mouse' is white-edged variegated plant.

Show us a few pictures as it continues to grow this year, please.

Pieter