You would be entering in a very busy market with no obvious advantages:
If you're using high power Cree type LEDs, then I don't see enough space for sufficient batteries so you'd have rather limited battery life. You could tuck a couple of cells into the bars themselves, but you'd have to drill holes or pass the wires under the grips, which would make mounting more tedious.
If you're using inexpensive and low-power 5050 LEDs, then you could use button cells in the lights themselves since they're low-power, but then you're rather restricted in terms of the max lumens.
Also, I don't see sufficient depth/space for sufficient optics. Again, not a problem for 5050s since they are so weak and diffuse. But for Cree-types, you need beam forming reflectors and optics.
So the final critical problem is that the consumer won't be able to aim the light laterally with Crees (unless you have movable optics inside). The angle at which handlebars are bent viz a viz the stem is variable -- from straight-straight to a small bend to a severe bend. Not a problem for 5050s with diffuse lighting, but most people want a sharply focused light that goes in front of them.
So I don't see how you're going to be able to do it with Crees. You can do it with 5050s but with the amount of diffuse light you're going to get out of it, I think your price point is < $50 for a pair, which is going to be tough to make any profit for you.
Additional back of napkin calculations for those who wanted to know if it's possible with 18650s:
Using a single Cree XP-G driven at 1000 mAh (250% luminous flux; about 300 raw lumens), you are burning 3.2 volts @ 1 Ah = 3.2 watts per hour. A high quality 18650 is 3.6 Ah @ 3.7 v = 13.3 watts. Boost driver efficiency at 85% gives you 11.3 watts, so you have just under 4 hours of time with an 18650 at full (250%) power.
Mountain bikes have a handlebar diameter of 22mm . 18650s have a nominal diameter of 18mm (i.e., 18-650) but are often closer to 19mm actual because of the insulation and power protection circuitry). It's a tight squeeze. It won't work with many drops.
It's doable, but you'd either have to have to customer drill a hole or pass the wiring under the grips. Having seen consumers try to install even basic lights that only require a single screwdriver, you're going to run into problems there.
Also, another problem that arises is how are you going to charge them? For removable lights, you can just take them in the house to charge. Many bikes are stored in sheds without power. Having to string a charger and micro-USB cable all the way to handlebars is going to be undoable for many.