I don't really know about I-Novae studies. Their program, Infinity, has a history possibly longer than Outerra's, and progress has been equally slow. Outera has surged ahead in the depiction of the planet earth and in the flora of the planet, while I-Novae has moved outwards instead and concentrated on outer space.
Outerra has incorporated libraries that allow for aviation, watercraft, and land vehicle simulation, whereas I-novae has concentrated on spacecraft and orbital mechanics.
Outera has introduced clouds and limited lighting, where I-Novae seems far ahead in both lighting, smoke and particle effects.
Are they rivals? They are procedural programs that seem to be heading in opposite directions, though its interesting to watch the individual programs evolve. I wonder if there is some innate difficulty that makes procedural worlds much harder than regular worlds to create. Things to ponder.