I, personally, would not say that the ultimate goal of Aikido is to become a form of meditation in motion. The ultimate goal of Aikido is as the word say, to be on "the path of uniting with Ki". Even the goal itself is a journey.. to the infinite.
As for meditation in motion, why yes, I do experience this with each training. Warning: I'm going to be a bit esoteric here, but it's the only way I could describe what was felt. Ever since I experienced training with ki-no-kenkyukai, there were certain changes in how I learn Aikido.
Everytime I partner up, what I do is no longer think how to, or try to find tricks, or just plow my way through. Relaxing, letting my weight fall naturally underside, keeping the centre, and extending Ki was the first thing. Sensing what the partner is feeling is part of the training. Making the partner comfortable as there is no threat coming from me. Feeling the surrounding, like the wind blowing behind my back, through me to infinity, this is my visualization of Ki.
The results are quite amazing. Technique-wise, from partners observation, it's as if they're the one falling down by themselves. Mentally, I've become more relaxed, and there was no frustration. At the end of the training, I felt more refreshed than I did before training, but yet not agitated or become hyped up, just a very nice comfortable feeling.
Do I believe Aikido is meditation in motion? Definitely, I've felt it myself. Do I believe that it's the ultimate goal of Aikido? No, Aikido's goal is way past that. Meditation in motion is still merely part of the tool. It's a long journey we travel on this road of Aiki.