The EM1 pretty much killed itself...
It had issues with LPR's reliability and was struggling to gain a foot hold in the market againts Bushys , shoeboxes and angels.. Same thing happened with the Rainmaker it was a novel idea and work well it just got crushed under bigger name guns.
As for further developements look for the "Raven Primal" It pretty much was a slightly improved Em1 made by Kingman later on.. I think 2005-06