Re: David's Drills
Yes, the aggressor can do all of these things - at least he/she is allowed to. If we see the aggressor not doing them it is more because they are being entered upon and having their balance broken in the midst of their strike and/or during their plans to execute the next strike. In other words, while the defender is not pro-actively checking against such things, the aggressor in his/her own aggression is preoccupied from doing such things.
However, I am sure one will get that practitioner that seeks more to NOT be taken off balance than to attack the defender - in which case the things you mention become more viable. However, such a student would come to face a lot worse hardships than being taken off balance come higher drills where the defender is allowed his/her own ballistic weapons.
It is not only therefore more conducive to this drill that the aggressor see it as his/her job to hit the the defender (fast, hard, and many times) rather than prevent him/herself from experiencing the kuzushi, it is way more conducive to other drills, and to one's survival rate in those drills, to have many hours of practice learning how to apply ballistic pressure on your opponent.
If a student starts to defend more against the kuzushi than put pressure on the defender, we simply allow the defender to strike. This always motivates the "aggressor" to be the "aggressor" again - funny how that happens. :-) Most folks however can follow the instructions - which were to apply as much ballistic pressure on the defender as possible. With the kuzushi being so gentle, the fear of falling doesn't play such a big part in resisting the instructions.
Anyway, I think if you look at the slow motion parts one can see that the aggressor is either in the midst of the strike he is throwing or his plans to throw the next strike when he is entered upon. In this way, we enter with a (type of) pre-awareness or we enter with a blending of uke's action/reaction. Martially, in my opinion, irimi requires both things of us in order to be a viable tactic - which is what separates it from simply moving forward or in.
I'll take two shirts and one hooded sweatshirt if you got 'em. :-)