Creatively, I think the Green Lantern franchise can only sustain two Green Lantern books: (1) a true solo, aka Green Lantern; and (2) a small team, aka GLC--which really needs compelling alien characters with their own development to be interesting. The anti-hero approach could work for other Corps, like it did for Red Lanterns, which didn't have very good art and could've gone further in the anti-hero direction. So maybe the franchise could actually carry three books...
A Sinestro Corps book could be similarly handled to Red Lanterns, but using fear to impose order seems like it would get old quickly, and outside of Sinestro who works better as a villain-- I don't think people are interested in the Sinestro Corps characters as leads. Plus, folks seemed tired of the rainbow corps idea in general. I can't see Sinestro or any other villain carrying more than a mini. DC has tried creating books around powered up Lanterns, like New Guardians, and the concept isn't different enough from GL or GLC to attract a notable readership.
Based on that, I don't think the franchise could handle more than four human leads: one for GL; two for GLC at most (if written as a mentor and mentee book); and one for RL/anti-hero group. That would be the absolute max, with 2-3 being more realistic. I'd put John in GL, Jessica and a mentor in GLC, and Guy in RL. The others should be retired, but I could also see DC choosing to use them in non-GL books like JL Oddyssey (not set up to involve 2814 or Oa in any way) or Young Justice (too young to actually be a Corps member). Sure it's not a Batman-level franchise, but I think there are usually only ever 4 Superman books going, and it's still at or more than the WW, Flash, and Aquaman franchises. Whoever's in JL should carry GL. Doesn't make sense to me that you wouldn't bring readers of one book to the other. Besides exposure and a shakeup, I think John makes sense because we know he's a Corpsman by design. He served in the military; is well educated and pensive but tough and outspoken; and cultured and socially conscious. It would be interesting to see him outside of the team context and get the personal development he needs.