It's clear from reading this that there is little agreement about what randori is much less how to go about training the skills. Discussions range as far as concerns for making randori less conventional, more like real self defense.
When I talk about randori I am talking about multiple attacker practice. The way I was taught single partner free style application was jiyu waza. Randori for me is the practice of Aikido waza applied in a multiple attacker situation with the attackers using conventional attacks (the standard stylized strikes and grabs of the Aikido repertoire). Aikido randori in the sense of what I am talking about is a stylized practice. It is not intended to be some sort of street self defense application (any more than regular one on one practice is about street fighting).
Talking about randori from the standpoint of non-traditional weapons, trying to make the attackers behave in a more "realistic" fashion, is perhaps an interesting practice but I do not consider this to be what is normally meant by Aikido randori.
Asking the attackers in an Aikido randori to act in a more "realistic" fashion changes the whole practice. I used to teach multiple attacker defense to police and security personnel. It did not look anything like an Aikido randori. It was based on fairly close quarters attacks by two or three attackers. The first person you touched you did your level best to disable with your first strike, you smashed him into the next closest attacker, smashing his head in the face of the next attacker if possible, Each person you touch needs to act as your defense against the next attacker. It requires total commitment and maximum use of the force available to you. Anything less than that in a real street multiple attacker encounter against committed attackers is likely to result in your death or a trip to the emergency room. I do not see this as Aikido. It is something else.
I think that Aikido randori is a form of "moving meditation". It can be full speed, full power but sticks to conventional attacks. It can and does include weapons... bokken, jo, bokken but once again, it is not intended as some sort of "realistic" practice. Three attackers with weapons, especially edged weapons, is going to be your death. Unlike that great fight scene in the Last Samurai, three attackers with swords or knives do not need or want to commit to an attack. They simply close in on your until there's no more space and carve you up. If you want to talk about "realistic" defense against multiple attackers with weapons, the only system I have seen that I think is very useful as normally practiced is the Russian Systema. But that is quite a different practice and while it might represent application of various principles if "aiki", it is not Aikido, in my opinion.
I also strenuously disagree with the idea that the way to get get at randori is simply to do lots of them. This is just a repeat of that old idea which says just do it a lot and you'll figure it out eventually. This might work for exceptionally talented individuals who are capable of being their own teachers but it is a very slow and inefficient way to transmit a set of skills. I have been holding multi day randori intensives for over twenty years. We have done thousands of randoris at this point. Every combination of grabbing randoris, empty hand randoris, knife, sword, and mixed weapons randoris you can think of while staying within the traditional Aikido paradigm.
There are patterns that recur over and over. You can see how certain types of movements produce fairly predictable reactions on the part of the attackers. This allows you to go from a reactive mindset to a mindset in which you shape the randori and take what is seemingly chaotic and unpredictable and make things increasingly probable. Randori is about creating time. The most rudimentary understanding of this is creating time by trying to go faster than the attachers. But that is largely not effective, especially if a randori goes on for any length of time. So, at the higher levels, creating time is done by finding various ways to slow the attackers down.
Every one of these things is a teachable skill. This does not need to be a process of each person re-inventing the wheel. These are discrete, practicable and teachable skills. If one wishes to make training effective and efficient, so that one gets the best results from every unit of time spent on practice, then one must be aware of and target the discrete skills one wishes to master. Randori is an area in which there is often a lack of thoughtfulness leading to a lack of a conceptual basis for structuring the practice. I had a young woman attend one of our intensives who had been told by the seniors at her dojo that "randori was doing the same things you always do just faster". This is so wrong that its stunning that seeing that there are yudansha out there who believe this to be true is depressing. It would be absolutely impossible to go about training ones randori to a high level with this type of mindset.
One of the real problems with Aikido as an art is the lack of a coherent conceptual basis as to what one is trying to do and why one is trying to do it. People mimic technique done by teachers without much of any explanation of the whys and wherefores. This leads to people not even knowing what is really working and what is not. This is especially true in randori practice. As people have stated, despite that fact that virtually every style of Aikido with which I am familiar requires a multiple attacker randori on their yudansha tests, very little attention is put on this area.
We have done so at my own dojo. I would say the one place with which I am familiar that has spent as much or more effort on randori is Haruo Matsuoka Sensei's dojo. I believe they are continuing a focus which they had in their practice under Steven Segal. Anyway, Matsuoka Sensei's randori demo at the Aiki Expo was, along with Kayla Feder Sensei's, absolutely outstanding. One could see him systematically using every one of the movement principles which we have identified and teach. It was controlled and intentional, at no point did he look like he was "re-acting" to his attackers but was instead "creating" those interactions.
Here are some examples of what I think represents great randori work. The Matsuoka Sensei video has a couple elements in it which were clearly choreographed for effect but you can see that the majority of it was spontaneous. The second video was from a dan test and was completely spontaneous.
Matsuoka Sensei Randori
San Dan Randori against jo, bokken,and tanto
As I said, I do not think this practice is about trying to be "realistic" as in street fighting. It is a moving meditation. It requires being totally "in the moment", at no time can your mind stop, you can't get stuck on any element... if something doesn't work as intended, you have to let it go instantly and be in the next movement. These are teachable skills... you can get a kyu ranked person to internalize the movement patterns. But the ability of the person to actualize what he or she can visualize in their minds is limited by their technical proficiency. Often you can see well trained junior people who clearly "see" what they are trying to do but they still can't make it happen the way they can envision it. So, randori practice always throws one back onto ones fundamentals which is another reason I like it so much.