I think I'm in the minority, because I didn't dig Flashpoint that much. I understand that they had to set up the world, but for me, the rooftop scene was a big example of why they say, "Show, don't tell." They told us a lot about the world, but we saw very little of it. I would have rather had a few panels (at least) of each of these characters doing something and then the rooftop scene in issue #2. I thought it would have been more effective if I knew (in the "Flashpoint" universe sense) these characters before I saw them struggle with this decision. It also would have been more effective, for me, if I saw the devastation in Europe.
It just seems that these alternate universes are similar in that we are shown drearier America and told that Europe is totally screwed. If memory serves, "Age of Apocolypse" did this, as well as the arc in Booster Gold where Booster saves Ted from dying.
For once, I'd like to see an alternate universe where things are better, not worse. I understand why they usually go with a dystopian reality, but it's a bit played out for me.
As for the line-wide reboot, I won't discount it, but we've heard rumblings of DC doing this time and again. Infinite Crisis was supposed to reboot everything and renumber everything, but it didn't (for the most part, Justice League of America and Flash did get new titles and new #1's).
While I can see them incorporating some of the Flashpoint Universe into the regular DCU, I don't see them rebooting everything. Grant Morrison seems to have plans for Batman beyond August and while Green Lantern may be in "epilogue" mode, I read its solicits as new directions for the characters stemming from "War of the Green Lanterns," not "wrapping everything up to restart everything." Plus the ends of Brightest Day and Justice League Generation Lost set-up too much for DC to ignore it in order to reboot everything line-wide.
Finally, I really hope they don't restart every series at #1. It would be a shame after celebrating Action Comics #900 to restart it as Action Comics #1