I believe this is where it was first hinted at:
There is no way the standby queue can accomodate two wheelchairs or ECVs having to pass each other to let one user leave. Those lines are no that wide. What a dumb idea.
forums.wdwmagic.com
The assumption being this played into their thought process on why they felt they both could and should change the system. Disney will easily be able to prove that people who can't get by without DAS were being negatively impacted by those who were using it who could get by with other accommodations.
That, on it's own, seems enough to justify the changes but they could easily include any operational and revenue impact arguments they may want to make as well.
ETA: Before anyone points it out, yes, I know in that case they are talking about the ability to ask questions specifically but the point is it allows for operational changes if it is helping reduce the negative impact to legit users.