Re: yet another annoying cross training q
What if you want to study bjj (in addition to aikido) because it's fun, challenging, to meet new people and to learn some groundwork?
Different goals in budo (martial effectiveness, learning how to use one's body, becoming better people, etc.) can mandate different paths up the mountain -- even if the end destination is the same -- the important thing being (IMO) that you are committed to walking the path -- and stick with it.
I think that to study bjj because your Aikido doesn't do groundwork could be a logical progression -- assuming three things: 1) You have a good base in aikido (subjective, yes, based on the person). 2) You want to learn groundwork. 3) Studying means you commit several years to the effort.
What I don't think is useful is . . . . studying a little aikido here to get some joint locks and throws . . . studying a little bjj to get some groundwork . . . studying a little escrima/arnis/kali to get some sticks and knives . . .
Eventually you'll just be a jack of all trades and master of sh*t.