Brown adipose tissue is “brown” because it contains lot of mitochondria, which play a critical role in turning food nutrients into cellular fuel (ATP). Brown-fat also plays an important role in keeping you warm when it’s cold.
You don’t need to wait for boffins to come out with a brown-fat-stimulating-drug, playing in the snow will cause the same effect! As your body gets cold, brown-fat activity ramps up, burning your body’s available/stored energy to generate heat, and heating up a person even just one degree takes a lot of energy. An person can DOUBLE their resting metabolic rate (the baseline energy required to keep you alive) by being in a cold environment.
This is one reason Michael Phelps needs a zillion calories a day. He’s training in lower-than-body-temp water for many hours every day, and his body needs thousands of calories to replace all the body-heat the pool-water sucks out of him. Water is >10x more thermally conductive than air, so if you REALLY want to max your fat-burning-fat you could soak in a tub filled with ice-water 20-30min every day in a fasted state. But I’d rather go tobogganing.