I had wondered about this at ODI level as well as in tests.
ODI's - Has the ability to bat through, just needs to work on turning the strike over better. Has opened in List A and T20's before.
Tests - If he opened, who bat 3? Taylor seems to be the obvious choice, but still think he goes at the ball too hard, too early.
But I like the potential of a batting line up of:
Williamson
Other Opener
Taylor
Brownlie
Ryder (or Guptill/Latham/Broom in the mean time)
McCullum
Watling
Good luck trying to get Ross to bat any higher than 4 - fits into the same category as Tendulkar, Kallis, Pieterson, Crowe, (the list is endless) best batsman in any team gets to chose to bat where they think they will score the most runs.
Fleming tried th approach, from 2004 onwards, of fitting the best 5/6 batsman in the side, rather than picking specialists for each position, it was one of several factors imo that lead to the dramatic drop off in our test performance.
Take a look at Sri Lanka for example they have been through a long list of openers in the last 7-8 years but Sangakara or Jayawardene have not moved up the order.
Personally I think if Brownlie wants to have a long term future in the side he should consider developing himself into an opener, with Taylor at 4 and McCullum at 5/6 his position will always be under threat from young talent coming through (ie Craig Cachopa), gifted strokemakers (Ryder, guptill), or the need to play a batting all rounder.
His other option is to score buckets of runs and lock his spot in.