It's a tough one. Is he the next best alternative, if you're giving Latham one spot? Given Brownlie isn't in the side, absolutely he is. Is he going to average 40? I hope so, but I wouldn't be laying anything down on it.
If he can average 30, great. I'd prefer to see him at 5 but Baz is there, and BJ can probably move up in future years to allow Neesh, Anderson and whoever else to clog up the middle order.
Agree with all of this and like your post. However I wouldn't want to give him a middle order spot. He needs to make it or break it as an opener for two reasons.
1) We can't forever be having our batsman shy away from the opening position especially if they are an opener in the plunket shield. We need someone in there even if they would score more runs lower down the order. And by the way everyone would score more runs down the order. Opening is a treacherous business. From a cricinfo query. Openers average 5 runs less than the batsman in positions 3 to 5. Now there is some self selection bias in that stat given that the better batsman scam there way out of opening but there is also truth to it. I would carry on but I would be telling you things you already know.
2) He isn't attacking enough to be a 5 in a test match. I want my number 5 to bat with a SR of at least 55 and preferrably 60. Martin had a go at batting number 5 and he went right into his shell and batted with an SR of around 30 (exempting his 180 against Bangers and Mash). He will bat faster this time around, but he won't bat with an SR over 55 I predict. And there is good reason for that. His selection of shots he can play along the carpet is limited compared to more classy middle order batsman around the world. When I think of Martin scoring quickly in an ODI a lot of lofted shots come to mind that he will simply cut out of his test match play.
The reason why I want my number 5 to be attacking is just a set image I have in my mind for each position in the order. The Strike Rates I want to see from the batsman are as follows:
1 - Don't care even 30 is fine with me.
2 - Ditto
3 - a low SR early doors in his inning but about 50 by the time he scores his ton.
4 - 50
5 - 55-60 - he needs to be able to dominate an attack and score freely.
6 - 45 -50 (he can afford to be a bit slower as he needs to be a man for a crisis)
7 - Will take whatever I get.