I cant see Brawn joining McLaren unless its to replace Whitmarsh (how likely is that given that there isnt any rumbles of that happening), otherwise it would be a significant step down in stature wouldnt it?
(It would be a good move by McLaren though if they could agree).
Given how much Brawn is on record as hating the Honda management style (and frequent trips to Japan) Im not sure he would jump back into that - if he was to get a senior appointment.
Im also not sure how JB would appreciate Brawn (even though fo course he wouldnt get much choice, but would McLaren want to upset their lead driver that much. Bit of a gamble to say the least) given how little he was valued at the end of 2009 by Brawn / Mercedes. (Yes I know JB was very public about "wanting a new challange", but I dont believe thats anything like the whole story).