This stat below ranks players by the number of wins they have over top 10 opponents in slams (courtesy of Ben Rothenberg on Twitter). Andy sitting in equal 10th place.
My instinct is Andy needs someone who has experience in that back end of their career as an older player, perhaps managing their physical side. A player who has been there and done it as opposed to just a coach. I also think it is about respect - Andy , I though, did ok on the whole in Oz, reaching a final, but clearly it is all about the slams for him over the next/final year or two of his career (my instinct is end next year if he stays healthy).
Not sure who is out there with that type of profile, maybe his ideal coach would be to ask Fed to coach him for a while!!
Seriously, a Lendl again, or an Agassi, those types of guys would fit the bill. Won't happen of course
Andy's instinctively too defensive ( to win the biggest prizes ) from very early days when such was his defence and adaptability that he could frustrate the very best, notably Fed.
But at Slams in particular he can get into long drawn out wars that way and that is even more of an issue at this stage of his career.
Lendl was the one man that got Andy to be consistently fairly aggressive and trade in a pragmatic way, if often not so interesting. Generally he was still too good, he won matches easier and he won Slams.
Don't think he'll be winning Slams again but I would prefer he didn't spend much of the remaining part of his career on the back foot to much lesser players.