IPS4 was released a whole year and a half after they initially said it would be ready, and yes they gave an estimated date. When IPS4 was finally released it was full of bugs that they just got under control recently.
I do not recall them having a due date set in stone for 4.0 and our shared experience may be different as I finished migrating around the time of 4.1 (mid-edit: There are 52 weeks in a year and at one point v3 was averaging a security update every 2 weeks. I think v4 is much better)
My only issue really with IPB4 is they still use CKeditor. This really does bottle down their page load. For testing (mostly just to see what it would be like), I removed their editor on my test site and IPB4 was extremely and impressively fast without it. I hope some day they realize their error in keeping with CKeditor.
That being said, I still would rather there not be an internal deadline