I didn't know there was a thread here yet...all my DISboards time has been devoted to the massive argument-um, thread - in the theme parks forum
So much to say and respond to...anyone who knows me knows I've been studying Fastpass and its effects for several years...
I have a moderately high confidence that this rumor is true, although the exact details might be off. Trustworthy sources are reporting it from inside. No bus drivers involved. This is in comparison to the rumors over the past several years of enforcement.
This is NOT being driven by any need to "fix" something that was "broken". This is being done in advance of a new program, sometimes referred to as "NextGen" and "X-Pass", which very few details are actually known outside of those developing it, but IS coming. The only component known at this point is it will include the ability to make some sort of ride reservation in advance. How, and if limited in audience who it is limited to, is unknown but it is
rumored to be rolled out to deluxe guests first.
It does NOT appear to, at least at this time, replace the existing Fastpass system, but will be in addition to it. And some aspect of it necessitates controlling FPs more than has been done in the past.
Fact: CMs are trained to accept late FPs (although it seems some of them forget this, or were asleep in class...

). And it isn't just in training - it's in the docs that are available to them. I've seen the actual doc, and there is now an image of it in the wild and can be seen in the other thread.
And there are mathematical reasons they allow it - because in the end, the number of people who actually use them late is small, and have little effect on the lines. And in fact, the standby line gets to go a little faster when a FP user doesn't show up on time. So to a certain degree things are actually better when people use them late. If you want to read a boring analysis, or need to fix your insomnia, follow the link in my signature, which gets more mathematical about it. (I do need to rewrite it one of these days).
Also, one of the greatest arguments is to why there is even a window if they didn't care of people used it, has an answer: it is psychological. Apparently in testing, people understood that they had more time to use the FP if they were presented a window, than if they were just presented with a "return after" time. In the latter case, more people would stand around waiting for that time to come.
Responding to some of the many posts...
Actually, they'd let you use them late no matter what. It's operational procedure. They will more loudly inform you you can use them late if there is a ride breakdown, but they don't have to change anything.
Unfortunately, these are more substantiated than in the past. There was even a test some months back where they were informing guests at some attractions that late FPs would not be accepted. They still accepted them, but they got information on how often and why. It was a data-gathering test.
You can't get rid of return times completely. Since it is available to everyone, then anyone could return any time they wanted - and they can already do that. It's called the standby line.
FP works by requiring the FP user to defer their ride time to sometime after they would get to ride if they got into the standby line, in place for not having to actually wait in the line. The rare occasions when the FP return time is sooner than the current standby wait indicates people aren't paying attention, or operational issues at an attraction that probably shouldn't have FP anyways.
Universal Express pass "works" because of the limited audience it is given to. There are two versions: the "resort" version which is unlimited, but only exists for resort guests, and the "pay for it" version, which is limited to once per attraction. There may be a premium "pay for it" option that is unlimited now as well. But in any case they can limit the availability.
That is part of the NextGen/X-Pass initiative.
What exactly are the rules? There are only two definitive rules: You can't use the FP before the stated time, and you can't use it on a different day. Late FP use is actually permitted within the language on the back of the ticket, and is part of the operational procedures.
That is an incredibly extreme example...but also, between noon-2pm, the standby line moved FAST. It's all a wash in the end.
On that last statement - if you are a CM, if it was in fact a rule that wasn't being enforced, I would expect the CM documents to say to accept them without any exceptions. It seems the "rule" was to accept them, not the other way around. That rule appears as if it is changing, and that's fine...but there will be problems.
This is also why I expect it is happening sooner than later. From what I understand managers will be on hand at the attractions, at least for a while, to deal with things, but the CMs will be enforcing and directing to the managers when needed. The managers can then decide on exceptions, etc.
It seems doubtful it will be that limited, because that isn't terribly useful. Based on some prototype screen shots, I think it will work differently than how FP works now, as in you won't necessarily have a specific return time, but perhaps set an order among a limited number of attractions. It may have changed and it was difficult to tell anyways.
If they do allow picking return times, they would probably be a separate set of return times than FP - something like noon-1pm is for X-Pass returns, and 1pm-2pm are for standard FP, etc. which could explain the need for more enforcement, but that is supposition on my part.