I think many people here will be interested in this. Can I request a little more information? The obvious question here is pay. How are you generating revenue? You refer to a 'freemium subsrciption service'. What is this? What degree of revenue are you aiming to generate (realistically!)?
The next question is how the profits will be divided. What percentage of these profits would go to the cartographer who created a battlemap in a given month?
I know you guys have done some pretty serious projects in the past (Open Gametable and the Core Mechanic spring to mind) so I'm sure this is well thought through. I'd be glad of any expansion on the compensation that could be expected from involvement in the project.