Well the customers that bought your rear arms and toe arms would probably like to have the endlinks also. The ones offered by competitors don't have the man power to mass produce the products. And as long as your endlinks are stronger than stock u might get more customers that just want to replace the worn out stock ones and last is that your purple is sick!
The front swaybar endlinks have a pretty short life before needing to be changed.
If you offered one that wouldn't need to be changed, I believe you'd have a pretty solid market.
Also, adjustable length would be a plus for us that have coilovers.