Well, this could go one of two diametrically-opposed ways.
McDonald's is currently product-testing mozzarella sticks in New York, New Jersey, and Connecticut, including at numerous locations in New York City. They're about 100 calories a pop and come three to a package, so it's not exactly a huge order. They're also apparently not safe for vegetarians for some reason (the nutritional info doesn't say specifically why not), so bear that in mind.
I also can't seem to find a current price point for them, so if any readers who live near a McDonald's that sells this would like to share that information (along with how they taste), it would be greatly appreciated. Kinja user naysayeristaken provided an image, which shows the sticks priced at $1 per three, which is actually a pretty great deal.
They've apparently been tested in the UK before, and were wildly popular. No word as yet on how long this is going to last, so if you're a fan of both fried cheese and intestinal distress, go nuts while you can.