Its been out for years, and successful.... For a reason.
Considering it's a pretty old case...I'd say it's sustained.
Here's the real question.... why do you want another load in this case?
Have you flown so many J510's your sick of it? If not, Aerotech isn't likely to listen.
Does this load's burn profile not fit for a flight you are planning and another propellant would? If not, why do you want another propellant? pretty colors?
Agreed. It's a unique load and one load itself supports the case. Having multiple loads for a case like this would likely HURT aerotech, not help it. It's a unique nitch, and I'm betting sells way way less motors than a case like the 38/720. So there just isn't the sales support for multiple propellants. You may see X sales with just the J510, and say, X+ 3% with two loads for the case. not worth it.
Now, yes...I'd be all over a green load in this case. But the number of people who SAY they want to buy a product, and then number with cash in hand when product hits the shelves, are two VERY different numbers. So, without real customers ready to buy.... AT isn't going to dive off into a small market load, thats a high investment in time and resources to develop.