I just don't think you are ever going to be able to balance the burden of responsibility in a party -- trinity or not. There will always been leaders and followers, people who step up and perform and people who just want to get by.
Giving DPS more responsibility is not going to do anything but force everyone else to carry them harder. And, if it ever gets to the point where they can't be carried, then people just quit.
Proof? 3.0-3.3X
I don't even think the current system is that flawed. I just feel like if you're going to force players to shoulder a bigger responsibility, then you're going to need to support them appropriately.
In principle, this isn't that different from many other aspects of this game. For raiders, if you're going to ask that they invest their time and skill, then some of them are going to expect to be rewarded. We saw what happened in Savage SCoB when they weren't.
Gifting 2 of the most popular jobs in FF history to DPS is not exactly a sign of support. Not releasing a tank or healer in an expansion is not a sign of support. Many have said that they're waiting to see what changes are made to existing tanks / healers but if the changes are merely a formality, then that won't be a sign of support.
A paltry amount of bonus gil or experience is not enough. Tank / Healer exclusive mounts only last so long. Fast queues is a meaningful incentive and successfully lures people to the roles but it's clearly not enough to bring some semblance of balance to queues. Then you have this topic trying to take that incentive away from the roles and assuming it won't make the problem exponentially worse.
Just look at DRK. The role was rewarded with one of the most popular jobs in the game and queues flipped on their head for a month+. I can guarantee that if SAM was a tank, DPS and healers would again have instant queues for everything.
This is a game of carrots and sticks. It's not that complicated. Like it or not, we live in the age of instant gratification. Expecting people to change is foolish.
What you're seeing with tanks / healers starting to charge for their services is the system correcting itself.