How large an army can the Riverlands have, post-Economic Development Plan? Does it stay the same as now? Or does it increase?

Keep in mind, the Riverlands ought to have an army 40-45,000 strong based on its population, but can only seem to muster 20,000 given its current state of development and political organization. 

So with proper development policies in place and a more effective system of government to bring the resources of the region to bear, I wouldn’t be surprised if you could get an army 50-60,000 strong.