I don't have any issues at all with McCullum opening. As someone who's done a lot of wicketkeeping (and has a bad back) I can understand entirely when McCullum says he can't continue to wicketkeep at test match level. I've had to give up keeping these last couple of seasons because of my back problems - unfortunately since wicketkeeping my strongest suit so I've been dropped down a grade because I can't justify my position on batting alone...
If you accept he can no longer keep at test level, I think he fully justifies his position as a test match opener. He's come off a poor series versus Australia, but to be honest outside of Dean Brownlie no specialist NZ batsmen had a good series. He also had a poor game versus Zimbabwe, but in the series before that he averaged 39 versus Pakistan, and 74 versus India (including a double century). I think technically he's one of NZ best batsmen, and would probably be my first choice as an opener at this stage. I'm not convinced about Guptill as a test match opener, but we really don't have any other options at this stage, as most of the first-class openers in the country have already been tried and failed.
I think the real question is who should be the NZ wicketkeeper. Reece Young has been pretty solid behind the stumps, but has struggled a bit with the bat. I get the feeling he will be maintained for the one-off test versus Zimbabwe, but if struggles again with the bat he could be under pressure to maintain his spot for the South Africa series. For me there are two obvious options to replace him: Kruger van Wyk or Derek de Boorder. Both a very good wicketkeepers, so it will depend on what the NZ selectors are looking for (and whether van Wyk wants to play for NZ, as he is still eligible for South Africa if he was wanted by them). van Wyk is a more attacking player who has good leadership qualities, and the ability to bat pretty high up the order, while de Boorder is a bit younger and is more likely to work the ball around, rather than hitting boundaries. Personally I favor van Wyk, but I wouldn't mind seeing de Boorder get a chance either. I believe both are more than good enough to bat at 7 (or 8 if they want to bat Vettori at 7) at test match level, so Young is certainly under a lot of pressure to score some runs.
Both Tim Southee and Doug Bracewell have the potential to develop into very handy lower order players at test level, and the likes of Neil Wagner can be pretty handy with the bat at times too. I think a batting lineup with 7. Vettori 8. de Boorder/van Wyk 9. Bracewell 10. Southee 11. Martin/Boult looks pretty handy. The problem arises when Vettori is out, as whoever replaces him is unlikely to be near his level as a batsmen, though I do believe that Doug Bracewell could turn into a genuine allrounder at test level.
