We also don't know exactly how Disney will charge guests for the option.
Disney's Magical Express is marketed as "free" but every resort guest pays for the service bundled into their room rates. WDW transportation (buses, boats, monorails) is "free" but guests pay for it via their ticket purchases.
Disney has been looking for a way to wean resort guests off of 20-25% discounts and "free dining" since the economy tanked in 2008. I can think of no better way than offering enhanced FASTPASS features for "free" to resort guests, while gradually charging higher rates to those staying in the rooms.
A lot of it may depend upon how much guest usage the FP system can support.
But all pricing discussion--including my own comments above--is purely speculative at this point.