As an aside, back a good decade and more ago, I had the opportunity to hang around and observe Rickson Gracie a fair amount, for a while. I watched him teach, train, and roll (grapple.) He was doing something that almost no one else I have ever seen in BJJ really does. Totally effortless, flowing, really amazing stuff. Shocking at times in fact, how easy it was for him. I would definitely call it Aiki in a practical sense. He wasn't manifesting "everything" that one might classify as "internal Aiki skills" but his ability to use the other person's intention, movement, and in essence, energy, was phenomenal. So, somebody out there, at least, has some sense of deeper skills and their application.
Similarly though to what some are pointing to in Aikido, most BJJ practitioners are not doing what he is doing, nor do they necessarily know that that level of skill etc. exists.
One thing he used to say, and this was not a mis-translation on his part, was "flow with the go" as opposed to the conventional phrase. I liked that a lot.
Two further (Potential) asides . .
1) For a long time (maybe still? I'm less in touch with those circles these days) - Rickson was considered by many to be the standard bearer for BJJ of his generation. His competition record across a number of grappling sports (judo, bjj, sambo, wrestling) is impressive, to say the least, add on to it his accomplishments as one of the pioneer champions of MMA outside of Brazil . . the question is a valid one - is he teaching people BJJ tm or is he teaching them to do what he does (or where's the overlap versus where's the gap, if any)? No dog or assumption in this one, just more questions.
2) There's been a number of conversations behind the scenes about some of the curriculum and training methodologies of BJJ at certain levels where there's "secret teachings" that may point to some training of jin and ki/kokyu. I know when Royler Gracie flipped me over from the guard years ago at a seminar, there was smooth movement and good leverage at least, but my uninitiated-into-any-explicit-internals self at that point didn't know whether it was internal strength or just explosive movement combined with good position. The level of sophistication and depth of internals in BJJ, who knows? But I think like many arts that come from older traditions, there was a time when it was more widespread and some things get emphasized/dropped/lost over time so . . *shrugs* . . . maybe yes, maybe no.