So putting 'attendance as trailing indicator' together with most families planning their vacation 3-6+ months out...that shifts the potential impact to the fall Halloween and Christmas 'upcharge season', which they've already announced prices and ticketing for. I'm curious about what kinds of discounts may be seen then, too. I'm also thinking that DVC owners who schedule far in advance aren't likely to cancel, but I don't know what percentage of their consumer base are DVC owners. Or intl tourists for that matter, although I think I've seen that intl tourists account for up to 1/3 of Florida tourists, maybe 20-30%. My notes say that in 2013 Brazilian tourists were 20.2% of FL visitors at 770,000, surpassing UK visitors (no source attribution).
I think you're looking at "attendance as a trailing indicator" wrong. People who have plans 6 months out are very likely going to keep those plans. The question is that what they're thinking and feeling when they return home from their vacation at WDW. It also depends on their vacation cycle. For example, some may typically go to WDW every year while others may have a 5 or 10 year cycle.
A really good time where they come back and are ecstatic about the time they have and the value that they received, may have them going right back next year or it may have them taking that 10-year cycle and reducing it to 5 years. This is good for WDW. If this is true across the board for most visitors then you have a kind of attendance compression that happens across the next few years. More people going more frequently.
An OK time and OK value may have them just staying put and continuing with their normal cycles. The ones going every year continue to go and the ones who do it every 5-10 years hit it at about the same rate.
The problem arises if people had a OK time (or, at least, not a great time) and the value just wasn't there. Most people think that if they're shelling out big bucks to Disney then they're going to have an awesome time. They expect that. With cuts, increased prices, and nickel and diming on things, they may very well leave slightly soured which would put their return trip, if they choose to go back, farther out and you end up with a long-term decompression of attendance.
The thing is that someone who started planning a WDW vacation today to go a few years out (with saving for it and all that) is still going to go but their attitude when they return is going to affect whether/how soon they will go back so I think if WDW's decisions in cuts in staff, quality, and price increases are going to have an effect they'll likely start around 2020 but even that will be offset by a bump in attendance for the 50th so it'll likely be after the 50th before there's an attendance drop. So think 5-10 years out instead of 6 months.
I think there's something else at play, too, which could hit them a generation out: Right now you have people in their 40s who grew up with WDW and have fond memories of how neat the MK was and remember Epcot being built and that being neat and DHS and DAK. Those people have kids who are, or will be soon, hitting adulthood and probably have similar fond memories. Somewhere in the mix, though, is a generation that has memories of stagnant parks, dated designs (Epcot FW being the most prominent), and stale attractions. I think that there's a generation in there where it's not a fond memory of WDW but more of a ho-hum memory. In addition to that, that same generation has fond memories of Harry Potter/Universal. To me that is something that could be an overall issue with a generation that doesn't feel the need or desire to head back (with their children) to WDW. It's not magical for everyone.
Of course, you could weigh all of this out with the increase in population and the limited availability of the parks. There's a larger pool of folks vacationing to draw from and they're only going to get so many people in the park on any given day AND it's pretty much a year-round vacation destination, now, which wasn't the case 30 years back, so it may just all balance out.