It's just not realistic to continue stories about IATA making money on this to enrich themselves.
IATA is made up of members that have to abide by laws of their states and collusion is frowned upon by enough of them that no group could possibly benefit directly monetarily,
In the end it's up to voluntary compliance with this suggestion so voice your objections by choosing your carrier as you do today.
What the carriers are hoping is that the passengers will rush to buy new bags fitting the new suggested sizes. If enough of you don't fall for this, the carriers will have to subcome and come up with other alternatives to charge you for carry-ons according to what the market will bear (some pay, others don't)