There's an interview on aikidofaq with O Sensei and Kissomharu together where they're asked pretty much this question. I can't remember exactly, but I think Kissomharu spoke about teaching Taisabaki, Ma-ai and then the first technique taught was a shihonage. It might not be precisely as I've described- my answer here isn't so much useful as a pointer to something interesting....
http://www.aikidofaq.com/interviews.html
andrew