I think the charging rumours revolved around another rumour.
Buses do not run between DTD and the parks, and at some point it was rumoured Disney could change that. (Didn't they even run tests ?)
The main reason buses don't run between DTD and parks is to avoid guests parking there to avoid the parks parking fees.
so IF (and that's a huge IF) buses resume Disney Springs to Parks operations, then it would make sense to charge for parking at DS. And it would also make sense to offer something like 3hrs of free parking at DTD (for example)