after reading everything it feels like the series most likely to end soon would be:
1a. kiyoshi - unless they swerve with something other than the great demon lord to fight or he takes what's her name or something to try to get kiyoshi to fight better it feels like it'd wrap up after thsi fight is over
1b. kill blue - the status quo is completely broken, so unless they're going to somehow make a new normal for the series it should end after this arc
3. basically every new series - the new batch of 4 doesn't feel like they're going to stick their landings except maybe kdg, otr and nice prison are in the most trouble just by having already run longer than the newer batch of 4 though
4. elusive samurai - this is mostly limited by how much history is left to cover, but it feels like it should wrap up sooner than later
5. blue box - i doubt it'll end anytime soon but it feels like it's reached a point where the plot's gonna be fillery and/or wrapping things up with the side characters until what's his name gets to his senior year tournaments and then it'll end

after those everything else doesn't feel like it's gonna end soon (although roboco could potentially end out of nowhere because it's the kind of series you can't really predict and the movie has been released)