I figure it could go like this;
DC still wants to use their lesser known characters *somewhere* because you never know when you'll be able to adapt them, and adaptation is AT&T's goal. Legends of Tomorrow is pretty much all B-list characters, Arrow himself is a B-lister, and over at Marvel we've seen huge success with the likes of Ant-Man and the GotG. So DC doesn't want to just throw Vixen or someone into limbo forever if they can avoid it.
Within the direct market, we'll see some B- and C-list characters thrown onto team titles and/or used as supporting characters in solo books. Maybe Vixen joins the League, maybe the Atom becomes Superman's new science guy, stuff like that. You have all the big name characters on the cover to hold up sales but at least some of the little guys manage to find a place to be as well. And I doubt the entire publishing line will be nothing but A-list titles anyway, they'll have a few books for lesser known characters too, in a half-assed attempt at variety if nothing else.
Beyond the direct market, the sky is the limit. Everyone knows the big names like Superman and Batman and Wonder Woman, but that's no barrier to them reading characters like Raven or Cass Cain like it is with the LCS. If DC is pushing into these markets, they're looking to snag new readers from different demographics, not keep us old bastard fans happy. So digital could provide books for Cyborg and Blue Beetle, the New Gods could get OGN's, and so forth.
Everyone's talking about how they think Tim will disappear, and maybe he will. Or maybe he'll get a YA OGN that explores what it's like to be the "forgotten middle child" of the Robins. Seriously, there are *no limits* here, and if someone like Raven can sell well, then anyone can. Are y'all ready for B'wanna Beast to be the best selling OGN of 2021? It could happen.
Some characters, maybe a lot, will spend a lot of time in limbo and only show up occasionally to remind everyone DC still has the rights to them. Which is no different from what we have now. For real, when was the last time Vibe showed up? This sounds like we're gonna see all our favorite C-listers go away, but those guys are, for the most part, already gone.
But what we're *really* losing is the idea of a big shared "main" continuity. The direct market will still operate in the shared world of the DCU the way we're used to, but it won't be driving the bus as the primary version of the DCU. Digital and OGN's will be self-contained, or share their own continuity, and some digital/OGN's could be set in the main DCU too (Naomi season 2 for example), but the biggest change we're looking at, really, is the idea of losing the "main" continuity in favor of multiple versions appearing at once across multiple formats, with little difference in how "important" one version is over another.