The seventh batsman - ODI cricket
Firstly, the "six can't do, ergo seven can't do" argument. The seventh batsman is not in the team to hit centuries or have an average similar to Sachin Tendulkar. His main purpose is to finish off matches which the first six may have brought within range .... and in case of batting first, ensure that slam bang in the final few overs can be handled by one extra bat rather than bowlers who hold the bat like Anil Kumble does. In my opinion, it is a very rare occassion (usually means the first six screwed up) when the seventh batsman gets to play more than 5 overs. Thus the seventh batsman usually has some additional forte to him ... coz he is not really in the team solely for his batting ... hence, he might keep, he might field very well, he might be an occassional bowler (different from all rounder) etc.
That is why in my opinion, Laxman and not Kaif is the seventh batsman. Ok, so I know Laxman bats at 3 and Kaif normally at 7, but the seventh batsman concept is not really about the batting position ... it is about the number of batsmen in the team. Let us not talk about Gavaskar coz when the regulars come back, he won't figure anyway. However Kaif and Laxman will be fighting to take two slots in the team and if a keeper has to come in, one of these two has to go out.
Laxman bats at 3 .... we have many who can bat at 3 ... Laxman plays brilliantly against Australia but against all opposition as a whole, he really has to show much more than he has as a specialist batsman in ODIs. He is a great slip catcher but in the ODI game, rather than all day long as would be in a test, the slip is going to be active only for about 15 overs. He doesn't bowl.
Kaif on the other hand bats at 7 .... he can swing a few towards the end and make many more simply coz of his running .... oh man, I am sure he was a horse in his previous birth. If we do indeed go with a 7 batsman formula, there aren't many who can play in that position ... Kaif hasn't excelled in this position but he has done enough to hold on to his position. In addition comes his fielding abilities which are really a bit out of the ordinary. With Yuveraj, Kaif really gives the inside-circle fielding an edge it never had (not in the Jadeja / Robin era who are our claims to fame in terms of fielding) and India can't afford to let that edge go.
So does a specialist keeper come in? According to me - forget Australia here ... against Australia, I would always play Laxman - if D. Karthick can make the same or a better contribution than Laxman in terms of runs scored (it is not about ability or style or anything ... quite simply count the number of runs) and keeps better than Dravid (and for a specialist keeper, that shouldn't be a big ask), then he comes in. We don't need Karthick to keep to relive Dravid ... Dravid has kept very well and though not a regular keeper, he is more than holding his own ... yes, it puts a big load on him but he is very well capable of carrying the load ... so just to lighten his load, we can't weaken the team by bringing in a keeper who bats like crap.