It seems to me like WB is keeping DC films in development without actually proceeding to make any they can't back out of aside from WONDER WOMAN II, AQUAMAN, SHAZAM and the JOKER movie. There's a lot of scripting and considering for BIRDS OF PREY, BATGIRL, NIGHTWING, THE FLASH, THE BATMAN (which may or may not have Affleck) -- but what it comes down to is that WB is unwilling to attempt a TRANSFORMERS-level superhero project after JUSTICE LEAGUE crashed so hard even Informant wouldn't defend the financials. Superhero movies that earn 600 million dollars at box office should be made for no more than 100 million dollar budgets and preferably half that.
In terms of what makes financial sense, WB are waiting, I think. They're going to wait for WONDER WOMAN II, AQUAMAN and SHAZAM's performances before engaging in anything beyond non-committal development. Given how badly JUSTICE LEAGUE did, I wonder if the DCEU is simply going to be waiting until enough time has passed to start over. They may make a third WONDER WOMAN, a second AQUAMAN, another SHAZAM -- building on what's already been built without throwing too much more money after what's been lost. I doubt they'll want to make THE BATMAN or MAN OF STEEL II on the blockbuster level that Affleck and Cavill level salaries would demand. The DCEU with regards to Superman and Batman seems to be going the way of the SUPERMAN RETURNS sequel -- it's just not enough of an earner to press forward on this sort of financial scale.
When the LOST IN SPACE 1998 movie failed, there were no sequels, but because there was going to be some time between the next iteration, there were some novels set after the film -- just to keep the copyright going and to earn some revenue. I don't see WB demoting the DCEU to novels, but it's going to be some sort of scaled back exploitation that won't be the bold, continuing adventures of Superman and Batman.
I imagine the DCEU closing out with a final WONDER WOMAN film before making a new attempt at a live action DC Universe. I wonder if it would spin out of the Arrowverse, but the Arrowverse probably has only another 4 - 5 years left before it too is laid to rest with a good finale.
The future may be in the DC streaming service -- TV level productions that, like DOCTOR WHO, eventually make the leap to the big screen. Thirteen episode shows at 1 - 2 million dollars an episode before a $30 million feature film emerging from the shows that can make 200 - 500 million dollars at box office and be considered a strong return on investment. Perhaps in 2022, when enough time has passed, a new Superman and Batman will debut on the small screen and lay groundwork for leaping to the large.