How would a mead fermented with beer yeast turn out?
People do it all the time. Just be sure to give it enough nutrient.
Keep an eye on alcohol tolerance of the yeast as well, and adjust your OG accordingly. The tolerance level isn’t set in stone and you may see a little more or less depending on the yeast (and honey).
Personally I’ve done this a few times. My favorite was a batch with just normal clover honey and White Labs American Hefeweizen Ale. It came in at the tolerance, right about 10% and was absolutely delicious.
We use a number of beer yeasts in our commercial meadery. They perform like wine yeasts if given nutrients and in their temp ranges. They are a lot of fun to play with and can allow for residual sugar at end without need to backsweeten. Nice way to have complexity.