The history of DC editorially since Crisis On Infinite Earths can best be described as an OCD sufferer who simply can't stop cleaning that spot on the carpet, time and time again, even though to everybody else it appears perfectly clean.
This is a group of people who, in the past 25 years, has gone through 5 or 6 different versions of who the founding members of the Justice League were.
This is a set of writers and editors who put out huge, company-wide maxi-series, seemingly just to address whether or not Batman ever caught Joe Chill.
This is a bunch of cats who are so obsessed with making Hawkman and Donna Troy's history make sense that they keep redoing it...and redoing it...and wait, this time we really have it...nope, one more time.
Seriously, 99.9% of readers would be fine with a "this is how it is," a nod and a wink to any inconsistencies, and moving right along. Not DC, though. They're constantly trying to make their past continuity "perfect" (as well as being in line with whatever the latest editorial whim is). They can't stop washing the carpet...
Which brings us to:
Except it won't, will it? After Zero Hour and Infinite Crisis, we know that DC is going to return everything to status quo EXCEPT they'll use the whole changing history business as an excuse to re-adjust whatever niggling points of continuity they feel are staining their carpet right now.
So, what will change this time? A reboot for the Shazam family? Sgt. Rock surviving WWII? Power Girl being a founding member of the Justice League? Yet another Hawkman tweak?
Whatever changes they make, though, you can bet that they won't be permanent. 3 months after Flashpoint, someone at DC will look at things and go, "Wait, that doesn't 100% work," and start to stare at that "spot" on the carpet again...