Its a common misconception that COIE 'rebooted' the DC Universe. Well, it literally did so in-universe after the battle at the Dawn of Time. But continuity-wise, COIE did not actually reboot the DCU. It rebooted a few specific characters like Superman, Wonder Woman, and much later, Hawkman and Hawkgirl. And these reboots in turn led to a lot of inconsistencies and retcons all across the shared universe. But 70-80% of past DC continuity remained intact after COIE.
I'd argue that the New 52 was a much 'harder' reboot, and even there you had Batman and GL retaining the bulk of their past continuity.
DC is simply never going to reboot the entire universe and start from Ground Zero, nor should they. Instead, over time, the importance of having a 'main' universe is what's diminishing...and most of DC's best work now (and even in the past) has been in Elseworlds/Black Label books set in alternate continuities/universes.
I think any reboots in the near future will just be streamlining some of the continuity rather than a full hard reboot.
“Somewhere, in our darkest night, we made up the story of a man who will never let us down.”
- Grant Morrison on Superman
That's really what most of them have been, ultimately.
The only line-wide reboots that really went beyond 'streamlining continuity' were Flashpoint, and the beginning of the Silver Age way back in the late 50's. The latter incidentally is probably the closest DC has come to an actual hard reboot, and even in that case Superman, Batman, Wonder Woman and a couple of other characters remained largely unchanged.
Of course.
My point was that this was still in a sense the closest DC has ever come to a hard reboot. (Of course, in some ways, it was the hardest possible reboot, since you literally had most of your characters replaced by brand-new characters with the same names and basic concepts).
There's never been a situation where DC literally restarted continuity from ground-zero across the entire line. They've done it for a few specific characters (Superman and Wonder Woman after COIE, LOSH after Zero Hour etc.) but never for the entire universe.
No reboot is coming. These past past years were deboots.