My take...
1. We'd have a very subtle and swift change into the silver age Cap'n,
2. Cap'n meets Cap'n E2 who is retconned into the JSA,
3. The Guardians ask "Must there be a Captain Marvel?"
4. Get ready, here comes the "Sandman" Cap'n Marvel!!!
5. "Mar-vell" who?
6. As a trial to see whether there is a market for that old horse Superman, DC publishes a similar character to Superman called "Supreme Man" and has him square off against Cap'n Marvel in his own book.
7. Cap'n introduces the "original" Superman on the cover of Superman's 1st issue since the 1950's.
8. "Shazam" the Movie
9. Billy and
??(fill in the blank): The New Adventures of Cap'n Marvel
10. Shazam:TAS
11. The Death of Cap'n Marvel!!!
12. The Reign of the (Lieutenant) Marvels
13. "The Misadventures of Freddy Freeman" (a la "Smallville")
14. Earth-Prime's Cap'n Marvel Jr.s retcon punch heard 'round the universe,
15. 4th and 5th attempts to re-establish Superman in the DCU happen concurrently - "Trials of Kal-El" and "Superman vs. the Superman Revenge Squad",
16. The long awaited "Shazam Returns" comes out, and fans up in arms over how much it is like the 1st movie. Singer's name walking close to infamy.
(Somewhere I missed "Cap'n Marvel's Pal - Talky Tawney", and "Life with Uncle Dudley", and Mary Marvel's "I am a curious... Black"; let alone the "intense dreams" Cap'n has about a certain Amazon.)