Do we know that there is actually any rampant enough abuse to need to manage it? Or is this more of a "I didn't get the nights I wanted, so there must be someone scamming the system" kind of thing? Do we really think there are people booking 40 nights at top properties?

I mean, a Gold is staying at Hyatt 4ish nights a year... how many of them do we really think have figured out that you CAN book speculative nights at all, much less have decided that they are suddenly going to spend a week at the PH Tokyo, unless they were already planning a vacation there. And on top of that will consider booking normally unneeded hotel nights to get to a FFN. Its definitely a Flyertalky thing to do, but for general society... I think its pretty slim.

Are we trying to manage a problem that doesn't really exist?

If anything, why not just allow one speculative booking at a time. You can hold one hotel for one set of consecutive dates. Once you've earned those required nights, then you can do another one.

I dislike the idea of requiring points to hold. I don't think think a Million Mile balance gives you a better track record than someone who's earned those points then spent them...so why should a point hoarder benefit if they aren't necessarily a better customer? In fact, I think Hyatt would probably prefer that you spend them.