I know some people feel it is has. They say that Aikido today is a result not of O'Sensei, but his uchi deshi. If that is the case the original Aikido of O'Sensei is lost forever. In line with that then, when Aikido is changed by the uchi deshi's, uchi deshi that Aikido is lost and replace by another and so along the chain. Now Aikido is subject to a speciation of evolution. I guess it is the way we (as individuals) look at things. What ever model we choose to follow, what ever way we look at Aikido be it evolution or not will lead us (individual) to the ends we (the individual) intended to pick.
My point is that it's each individual's responsibility to try and take Aikido beyond what Osensei ( or his students ) did. This is also Aikido evolving.