Well, pretty sure the Devs are still saying the same thing to this as they were so many months ago.
Say you're an Ork Slugga. You get a killstreak of 20 or you stay alive for 2 hours. Imagine you'd grow a from 1 meter, to 2 meters to 3 meters - Devs would have to adjust every single armor piece and the likes for each of those "growing milestones". So standard Ork boy Helmet 1, 2, 3, 4 and so on would all have to be adjusted and fit for "Milestone 2" and so on.
Pretty sure that's pretty damn accurate to what the Devs said.

All in all, it requires a huge amount of work and would definitaly take long to do.
Growing could be pretty cool, yet as they've said we're going to be Ork Boyz. Not Nobz, but I definitely support the idea of specific Leaders being larger. Of course, Warlords and War council would be bigger.
Yet that would be for Open World. What about the Instanced World? How would this work there?

ork size based on the rank will change, so a nob is bigger then a boy.

Growing tho mid game is not happening

According to Xenology, Orks grow from combat because their body rewards success with a growth-spurt.

My suggestion:
As you progress, you can unlock "body-parts" that are really armor-components that get slapped on your body. You would essentially be a skinny Ork that wears muscles as armour/clothing. (Well this would only make you broader.)

An alternative would be going by skin-color, where you start out as an Orkboy with a light shade of green and as you progress you get access to character-skins with darker and darker shades of green. (It would be hard to tell when you see a single Ork, but when you see a whole group of them, it would become visible who's a veteran and who just crawled out of their cocoon.)

If I can rank up into Nob height then I'm happy

It's the easiest way to show progression and rank in Ork society so I don't see why not have it as you level up you grow.

As an ork fights and wins, they get bigger.
As a player takes games and wins objectives, they gain the ability to play as nobs and bosses.
Nobs and bosses are bigger orks.
So you get to play bigger orks by winning more fights.
Which means the more you fight, the bigger the ork you are playing gets.
So the feature is conceptually already in the game.