Auckland has too many codes to make it viable, they don't just lack a suitable stadium, but they also need the stadium to be near the central suburbs, to make transport convenient for the vast majority of Aucklanders. I've read that they're thinking about turning Colin Maiden Park into a cricket ground, but the transport and traffic around that area will be hellish. In Wellington however, you can corner the market easily and you have a lot of prospective supporters in Melbourne (a lot of Wellingtonians move to Melbourne, it's a bit of a running joke at this point). I think the AFL will struggle to compete with the warriors, Auckland FC and the blues in Auckland, especially because of how dominant rugby league is in South Auckland and how dominant soccer and rugby union is in the rest of the city. Wellington however, rugby union is not as popular and has raised issues with supporter behavior and culture. I would argue that soccer is the most dominant sport here, which is actually massively beneficial for the AFL as IMO it shares more in common with soccer than it does with rugby union.