I think you're overestimating how many away jerseys they'd be likely to sell.
I can't imagine having a green one rather than a white one would make much difference at all.
I think you don't understand the point. The ARU have not an away jersey ATM. They made one for the WC because is a law but after the WC they will remain only with a home jersey as usual.
That's the first step, make an away jersey for every season, not just for the WCs. Look at South Africa. They wore against the Argies in Buenos Aires their away jersey. The Pumas don't wear a green jersey. Why they wore an away jersey in Argentina? Just for marketing, just for money.
The NZRU did the same with their away jersey. Even The Pumas, they usually wear their away jersey in Australia, they don't need wear it because the Wallabies jersey is yellow but they wear it for marketing.
I'm not talking about a HUGE investment, every nation has an away jersey. Even Tonga or Samoa. Make an advert with Israel Folau wearing a green away jersey and you can sell hundreds/thousands among League supporters.
Of course, isn't the salvation but is a step forward. Little things make a different. The risk is low and the gain could be high.
No need to wait to face Romania (yellow vs yellow) to wear an away jersey. Look at the Boks in Buenos Aires and the Pumas in Australia. It's a smart marketing move IMO
It's just a marketing move. Marketing = Money. Look at the NZRU:
The ARU need to improve their marketing department. I can't believe this. They don't sell away jerseys (Just for the WC) while everybody do it! Even tiny islands like Tonga!!!!