Re: Is two Days a week enough?
The fact that people have lives outside of Aikido shouldn't bar them from testing for Shodan (or higher Kyu ranks). If you can only train two days a week, you can only train two days a week. If it takes longer to get to Shodan, so be it.
Some people are willing to make Aikido the focus of their lives. Some have higher priorities or simply see Aikido as a hobby that keeps them active.
Obviously two days a week isn't going to be sufficient to "master" the art, but I would guess that a big chunk of those practicing Aikido want to be proficient, not a Shihan.
In my own case, I am only able to formally train 3-5 hours per week, but I put in effort outside of the dojo. Is this sufficient amount of time to get me where I want to be skill-wise? Definitely not. However, work/family/school take priority at this point in my life. However, the training time I sacrifice now is allowing me to put myself in a situation where I can train at a very serious level.
Two days a week is certainly enough to progress in any art as long as the time is well spent. You have to get on the mat with intent and focus. You can't let yourself go through the motions. Self-motivation is essential.
In regards to Ledyard-Sensei's comments regarding failing students who are meeting testing requirements, I am in completely agreement. If you don't have the skills, you shouldn't get the rank.