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.
We certainly have these discussions as well with my dojo mates. I think we do need to look critically at this issue and constantly re-evaluate what we are learning and if it is reaching our desired goals. Many of my sensei and instructors within my organization go to other practices, tai chi, BJJ, koryu, and Bujitsu with Akuzawa and look at them for new insights and understandings. We then synthesize those things back into our practice of aikido.
BJJ and Judo have had a profound impact on my understanding of aikido and aiki in general, and I can tell you that I probably won't practice aikido exactly the same as maybe I was taught as I may use different teaching techniques from time to time to teach aiki principles.
There are some aikido methods that I have employed in teaching BJJ that I think aikido does a better job of transmitting.
Semantics maybe, but I don't see what I would do as evolutionary as we are not changing the core measures and principles of aikido.