Honestly, I'm shocked that Disney didn't introduce, and even keep, FastPass+ as a on-site only perk. (And I'm someone who isn't a fan of Disney resorts.)
The per day guest numbers would have been much more manageable, even at peak times, allowing for tiered FastPasses per resort category (e.g. 3/day if you're at a Value, 4/day at a Moderate, 5/day at a Deluxe, perhaps even more if you're staying concierge), flexible park hopping even at launch, and addressing just about every other common complaint seen here all WITHOUT dramatically increasing standby wait times (since you're dealing with a smaller subset of guests) and even without needing to add FastPass+ to so many attractions.
I get that was done partially for crowd management, and to increase usage of so-called secondary attractions, but given attraction line re-dos, Cast Member re-training and other costs, coupled with the fact that they operated at high crowd levels without that sort of shifted management needed, for decades, I have a hard time buying that was the most critical reason. Literally needing more FastPass+ to feed to the masses was.
Yes, Disney needs off-site guests--last I heard anywhere from between 60-70% of people in the parks on any given day were staying off-property--but they also make substantially more, per-customer, from on-site guests. Given the precedent set by other parks, including Universal's Express Pass, and Disney's own logic that only half their guests utilized the previous incarnation of FastPass, turning FastPass+ into a resort-specific perk would hardly be beyond the pale. Especially if they had introduced it slowly (again, probably by resort category) and then gently phased out legacy FastPass.
Heck, given their monster resort room capacity compared to Universal's relatively meagre supply, "selling" FastPass+ wouldn't even have to come into it at all. Sure they COULD market it a for-cost system for day guests or APs, if they wanted to, but making it a resort-only perk would likely increase their occupancy even if they raised their rates, likely making it profitable to continue to expand their room inventory. And, yes, people buying "throwaway" rooms for a day or two of FastPass+ use would likely become common, just as it is now at Universal, which also wouldn't upset Disney one little bit. They get the revenue from a room without actually having any wear and tear on their property AND incur decreased employee costs, due to lowered service requirements. Win-win.
To me, the above would make SOOOO much more sense than what Disney actually did even if I, personally, still wouldn't like it.
EDITED TO ADD: My answer to the inevitable question of, "Do I think Disney doesn't know what they're doing?" And that answer is, generally no, but in this case, yeah kinda'. I say that because my guess, and it's just an educated hunch, is that their financial projections when approving this project wildly overestimated the value of the metadata they are now collecting on customers. This guess comes seeing many, MANY companies, investors and industries in the current age of the Internet fall for wild over-exaggerations of the financial value of knowing everything about their customer and how it will lead to increased profits. While it definitely leads to increased knowledge and certainly has some value I think real-life use-cases across diverse fields, from Facebook to Whole Foods, is showing that minute customer tracking is not the windfall that was predicted. It is labor intensive to collect and sort the data mined, cost prohibitive to selectively curb your product and presentation to suit individual customer's styles and only marginally financially successful no matter how much time and money you throw. In real life usage targeted marketing has a much lower return on investment than in almost every model I've seen, across a wide range of use-cases.
