What if somehow the deal that saw Marvel sold to Cadence and (eventually) Martin Goodman out of the company had gone wrong in some way? I don't have a single pivot point to make this an honest to goodness alternate history, but let's just assume Marvel was crippled sometime in the early 70s, and DC was the beneficiary of an influx of young talent needing jobs. This talent glut may have also weakened the hold of DC's old guard editorial, opening up DC to innovation that were definitely needed.
In one sentence: What if 70s Marvel had basically happened at DC?
Now, since this is ostensibly a gaming blog, I am more focused on how certain storylines or character intros might have transpired at the Distinguished Competition more than "wouldn't Batman have been great under creator [x]?" mainly because I think that focus is no less interesting, and more supers rpg gameable.
Here are some highlights:
Starlin takes over Green Lantern after the commercial failure of "Hard Traveling Heroes" and goes cosmic. GL battles a new assault by Darkseid (Starlin becomes the first writer to tackle the Fourth World after Kirby's series ended) and eventually even gains cosmic awareness through an encounter with the being that first set the Guardians on their path.
Steve Gerber brings his off-beat style to a revival of the Doom Patrol, and makes the adventures of the Swamp Thing even stranger.
Len Wein and Dave Cockrum bring some new members to the Legion of Super-Heroes, and Claremont follows for a long run. He also pens the limited series, drawn by Frank Miller, that makes Timber Wolf a star.
That's just for starters, but you get the idea.