If the "non-uber planner" that you mention, is concerned enough about a cancellation fee to not book a reservation, than this new policy is doing exactly what it's supposed to do. It is keeping people from making frivolous or duplicate dining reservations that aren't sure they are going to use.
In my mind the risk to Disney isn't at the time time of ADR placement, it's at the time of DDP selection. Right now with some work the DDP can be a moderate "value" (compared to Disney list prices). The real world evaluation seems to show it as a push bet at best on average (and this makes sense as there is no incentive for Disney to offer it otherwise).
That DDP buy-in is a large chunk of incremental revenue (or discount avoidance) for Disney. If the ease of making same-day/walk-up reservations really does improve then this may be a net positive.
However, it's very well demonstrated that people are far more adverse to the risk of loss than they are drawn to acquiring gains. The psychological math that goes into win/lose thinking isn't rational. People who were weighing potential gains (savings from list costs) vs. limmited flexibility, and now a penalty may opt to keep their money in their pocket until it's time to eat. We KNOW most of the time this means they will spend less with Disney.
Will filling previously full tables with short-term reservations offset that difference? Maybe. Disney must think so, they must have plenty of stats folks.
Of course it also means they're leaving money on the table. They just need to decide if it's worth going after by increasing capacity, managing their walk-up (non-reserved)capacity, releasing dining slots incrementally instead of all at 180 days, breaking out the DDP ADR pool from general ADRs (this makes it trivially easy to limit multi-booking or offer a single "vacation-your-way" penalty exception), and so forth.
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