I understand the reasoning here, but I disagree... shimewaza when done properly can be done standing, from all four directions. Success is dependent, as all waza should be in my opinion, on properly applied kuzushi principles, taking the sente and keeping it.
After thought... of course, this really comes down to what brand of aiki practice you're training in and what their practice methods are like. Nothing disparaging intended, by the way... just different strokes for different folks.
I didn't say it couldn't be done, I just said it is much more complicated and much less practical than say dumping them on their butt. I do however agree that with appropriate skill, you can choke a guy from standing. It seems to me however, that aikido was about trimming the superfluous techniques as part of it's creation. While choking is a great balancer on the ground, there are much easier and more efficient ways to balance the situation on your feet. Which is why I think standing chokes are largely ignored in all but the most showy of martial arts.
Again though, just personal opinion.