So, this is something I have wanted since the early/mid 90's elseworlds annuals. DC did this for all annuals that year, and it was pretty damn cool. With the possibilities of zero hour then 10 years later with infinite crisis. However nothing. Then a few years later, we were given Multiplicity. Loved it, loved it loved it.
Shortly there after, Convergence. Now the possibility to show points fom all time, charecters for everyone. Man.
So, I would treat it as a rotating title. Through single issue or three issue arcs. Multiple earths, multiple writers/artist. This could be an amazing title. Lots of fun. I truly believe this is a missed opportunity. Look how well received Dark nights metal was. It has spawned a mini series and already mentioned in the Arrowverse.