My opinion: highly unlikely.
It's anything but a trivial venture. BATFE licensing and inspections. Sourcing materials/ingredients. Waste disposal---like it or not, EPA is going to be part of the venture. Marketing and distribution---what can a new company bring out that will cause all the (rocket)boys to flock to your yard for your new milkshake?
The motors would probably need to be quite different from current offerings to have any chance of success. Or they'd need to be much cheaper than Estes et al. Quality assurance. Safety for the workers. Custom manufacturing equipment.
What motors are you looking for that aren't currently available? I know that some rocketnutz have expressed interest in something similar to the old blackpowder B14. Others have longed for a rebirth of Rocketflite BP motors in F, G, and H impulse. But I very much doubt that the interest in those motors would be sufficient to keep even a small company afloat. (Remember that although you can buy and store up to 50 lb of BP without a permit, a BP rocket motor with over 62.5 g of propellant still requires that the buyer have a BATFE license/permit/whatever. It's the gummint, it ain't spozed to make sense.)