Thanks for the comments. I would add to what Kevin is saying with a couple of things....
In application, submissions are really dangerous creatures. The level of investment to pull off a submission can be enough to affect your focus, your movement, or your energy. When you look at MMA work, you can sometimes see how [over] investment in a submission works against the submitter, especially if that combatant expels his energy unsuccessfully or allows his position to be compromised. Second, submission puts you smack in the middle of sport fighting and now you are back to looking for some obvious mechanism to determine your state of control.
Also, I saw a couple of posts about aikido pins not working. First, aikido pins work - proper control over the body will be reflected in a pin. What we are really talking about is that we have trouble successfully pinning our partners using aikido pins. This comes back to my first post about our partners needing to be honest with themselves and applying the proper filter to realize how their bodies would be damaged by non-compliance. For example, my partner has a lot of confidence that I will not dislocate her shoulder when I apply ikkyo pin. If my partner exploits that confidence, she can successfully defend against an ikkyo pin. However, in exploiting my trusts, she is neither being honest with me nor is she understanding the the potential damage her body may incur if I choose to apply the pin more severely. I think the problem lies more with uke and nage not doing things right, rather then the claim aikido doe not have functioning pins.
Pins are reflective of control. When you have partners contesting pins, ultimately your partner is saying, "I don't think you control me." So we need to change that dialogue to more clearly express to our partners that we do, in fact, control them.
And if you ever think the aikido pins are soft, ask a Daito Ryu person to show their pins, which are the parent pins of aikido. I have included a link to some of Kondo Sensei's group doing some ikkajo series work. You'll notice several uncomfortable pins that are all perfectly "aiki":