The first question that came to mind when I saw this thread was does the Arrowverse need to survive? Maybe it's simply ran it's course, and if that's the case it's had a pretty good run. I mean, the shared universe is heading toward a decade now, and it's not the hot new thing anymore. I think what it was able to do, mostly impressively early, has become a bit old hat now, especially now that Marvel is back in the game with WandaVision and Falcon & The Winter Soldier, with Loki and all the others coming up. And even within their own corporate house HBO Max now has Titans, Doom Patrol, and soon will have Peacemaker and a Green Lantern series, and HBO Max can push boundaries that the Arrowverse can't, and that might be enough to get some eyeballs who have become bored by the Arrowverse.
My love for it as waned over time. Loved the first couple seasons of Arrow and was impressed by The Flash as well. Also really enjoyed the first seasons of Black Lightning and Supergirl. I was iffy on Legends and let Batwoman go after the pilot episode, though I did see the first season finale in preparation for season two, and I've looked at it off and on. Black Lightning started losing me in the second season, though I do come back to it from time to time, and have looked at most of the final season. And Supergirl started losing me in the second season, but Lex brought me back for a while, but I can't recall if I've looked at even one episode this season. Superman & Lois started off better than I thought it would, but do I have high hopes for sustained success? Not for me, because I've generally liked the first season of each Arrowverse show so S&L so far isn't out of the ordinary there.
One of the issues is that these series go on so long that everyone becomes superpowered or a superhero and that crowds or takes away from the central character. Another is that the shared universe doesn't have anywhere to go after "Crisis on Infinite Earths". They could do the other "Crisis" books but it won't be as special as the first time, and I felt they flubbed the first time. I don't down them too much because I think they really wanted to give the fans what they wanted, and I loved some of the cameos, but their reach exceeded their grasp.
I don't think the Arrowverse can be saved, but the question is an intriguing one, so I'll attempt to rescue it. I like the idea of starting from zero, but I would not cancel all the existing series. While they have declining viewership, there are still viewers out there and fans of each series.
Instead I would try to usher them into where I was going with them by doing some retooling and soft, or not so soft rebooting, and Arrowverse 2.0.
-Saying all that, I would bring Flash to a close next season. And I would start looking toward the end of Legends as well.
-If Superman & Lois are the hot ticket right now, revolve the Arrowverse around them, like how it revolved around Oliver in the past.
-Batwoman: I would turn Batwoman into the gritty, dark, vigilante series that's been missing since Arrow's first two seasons. I also would look to Black Lightning and get some of their writers because they know how to craft better written black characters and mix in discussions of race and black history/culture than I've seen with the Batwoman writers thus far. Basically Superman/Lois and Batwoman become what Flash and Arrow were for Arrowverse 1.0. For those who might be put off by the exploration of race, gender, and sexuality, they might stick around because of stunning, brutal action, and some vicious takes on Gotham's criminals. If that doesn't work for Batwoman, I would do a Kate Spencer Manhunter series (ignoring the Arrowverse version of Spencer that's already there). I also wished we had gotten an Emiko Green Arrow sequel series. The proposed Painkiller series might already fit this bill, however, I feel Batwoman needs more of an edge.
-Swamp Thing: I would bring Swamp Thing back. They don't really have a dedicated magic/horror series, and Swamp Thing could fit the bill.
-The Atom: Can't have magic without science, and I wouldn't mind seeing a Ryan Choi series that also fills the gap left by Flash when it comes to a more science/science fiction based series.
-Amazon: I thought this was an idea they should've gone with. Not sure who was supposed to be the main character, but I would've gone with Cassie Sandsmark.
-Justice League crossover: If there are no plans for a League movie anytime soon this could be the next crossover, and it could bring back Flash, Black Lightning, Supergirl, Martian Manhunter, and other legacy Arrowverse characters.
-Not sure what I would do about Painkiller, Naomi, and Stargirl in my imagined Arrowverse 2.0 I'm inclined to keep them to see how they fare, because having younger skewing characters is a good idea. I think a Young Justice live-action crossover or series could be neat, and also a chance to bring back Thunder & Lightning, Kid Flash, and others.
-Loved the ideas about a Static and Question series, though I think Hardware could work as well for bringing in a Milestone character to lead a series.