It would be infinite (or pretty darn close). It would be divided into "strands"/regions. All of DC's different continuities would be in this multiverse. The main strands of the DC Multiverse would include:
1.) Big Bang style; Earth-1, present day is 1965; Earth-2, present day is 1945.
2.) Pre-COIE; neither COIE nor the events leading up to it happened hare. This strand is intact. Its present day is circa 1980.
3.) COIE; This is where COIE & the events leading up to it happened. This strand has "gaps" in it, due to 3,000 of its universes having been destroyed. Its present day is circa 1985, right _after" the battle at the "dawn-of-time".
4.) COIE Aftermath; The DCU introduced in issue #11 of COIE, its present day is circa 1985-86.
5.) Post-COIE; First seen in issue #1 of Man-of-Steel mini-series. Present day is circa 1990-95.
6.) Post-Zero-Hour; Present day is circa 2003-05.
7.) Post-Infinite-Crisis; Final Crisis also happened here. Present day circa 2010-11.
8.) Flashpoint.
9.) Nu52.
As well as all of the other media adaptations of DC characters.