???(Am I missing something here?) I'm surprised....how many sempai and sensei finds themselves, at one time or another thinking to themselves (or even saying),"I know this concept, but how can I possibly teach it to that student." How much time (and students) would be saved if students could understand concepts sooner and/or easier, without frustration.
There are alot of sensei out there that DO teach things like this to their students. Don't assume that just because you have not experienced it that they don't cover it.
Check out Roy Dean's website. He is a good example of a "crossover" that combines BJJ and Aikido. Although I think you will find that he too considers the two methodologies somewhat separate in training and not as a complete hybrid blend.
In randori and sparring maybe, but in practice (kata), you have to train them as separate and distinct methodologies in order to benefit from them I think.