I'd much rather them say fuck a connected universe and tell standalone stories with these characters with filmmakers who don't have to bother with Easter Eggs or worry how it messes with Shazam. Maybe they can franchise individual characters, e.g. a Superman trilogy, but I don't need to see him hang out with Batman.
Nothing about why any of the DCEU movies failed had anything to do with them being in a shared universe. They were just poorly conceived, poorly written, and poorly executed movies all on their own. So making future movies not be part of a shared universe, but not changing anything about the flawed way that they conceive, write, and execute their movies, is sort of like putting a band-aid on someone's finger hoping it will heal their broken leg. The shared universe isn't the problem. In actuality it might have been the only thing that worked in any of these movies. Shit, break it down.
Man of Steel - had a couple of Batman Easter Eggs and a few background references to other characters. Were any of those things the problem with the movie?
BvS - The YouTube scene was hilariously bad, but again - is that 90 second scene why the movie failed? Of course not. Most people agree that Wonder Woman was actually the best part of the movie, stupid theme song notwithstanding. Most people also agree that Batman's dream sequence with the Parademons and the hints at Darkseid were also great. Even the Flash thing was a cool easter egg. The problem wasn't bringing Batman and Superman together in a movie - they actually meshed very well as characters and looked "normal" standing next to each other. The problem was that they hadn't established either character enough, nor had they given them a reason to fight. And of course, they woefully miscast Lex Luthor and wrote his character about as poorly as they could. But take Batman and Wonder Woman out of the film and Lex is still a poorly written and acted character, and Superman is still all wrong, and still ends up being killed by Doomsday. All of those things were wrong. Even if it was the second movie in a Superman stand alone trilogy, killing him was always a bad idea.
Suicide Squad - There's no question the Batman and Flash cameos were some of the best parts of the movie. The post credits scene was again hilariously bad, but it would be pretty dishonest to say it ruined the whole movie.
Wonder Woman - the framing sequence with "letters from Bats" was weird and stupid, but I actually had to stop and try to remember them. I guess without the DCEU connections they could have set it in modern times, but would that have made the movie better? I don't see how it would have.
Justice League - again, when the characters all got together they meshed pretty well and it felt
The problem wasn't bringing them together, it was that they didn't establish three of them, and one of them was fucking dead when the movie started. Also, they tried to pretend Batman and Wonder Woman had this deep friendship that they also never established.
Rather than make broad statements, I prefer to look at each project individually.
I think they're making a mistake setting Wonder Woman in 1984.
Aquaman could be decent and there's no reason to jam in cameos or Easter Eggs. The movie takes place underwater for the most part. Fine.
I'd rather Shazam not be part of the DCEU in the same way I hope Deadpool stays on the fringes of the MCU. Like he can be part of it, but he should never be in a Justice League movie. Kind of like the Netflix shows and the MCU movies. (That's a bad example because I really want Daredevil to be in a Spider-Man movie.)
I think they're making a tragic mistake with the Joker standalone movie(s).
I think they're making a mistake if they don't tie a Supergirl movie into Superman and the DCEU.
I'm ok if they use Reeves' Batman to establish a separate Bat Universe, even Bruce Wayne is the only Bat person in it.
I also don't see the harm if they use the movie to soft reboot the character - making him younger but still part of the DCEU. Marvel recast the Hulk and Rhodey after all.
I think there's a lot more that can be done with Superman and hope they bring Cavill back, as he's not too old just yet. But if they decide to recast, that's fine too.