4 characters that you need to solve their story archs
That turns into less a "Maiden" issue and more of a "Character" issue, and I disagree besides. Winter was always a side character. She'll probably remain a Penny-like. Raven, despite my views on her, suffers from the same issue. As far as the plot is concerned she is always a second character to someone else (to Cinder's plans, to Yang's wishes). The Missing Maiden has never been important, and it would be an absolute literary disaster to introduce her, make her a main, and resolve her in the same Volume. I will have to concede on Cinder, though, for better or worse, she was always a main (weirdly Salem appears to be her second).
What will happen to the maidens in the end?
You assume something
must happen. Why? Right now they are as part of the world as the air. Not a single character in the show (of which at least two could) have shown any desire to reverse this. I don't see a reason to create faux tension in the final stretch. If they ever want to try that idea out, they can make a book about the maidens.
What will happen to the powers once they defeat Salem? Will the powers change hands during the story? If so,how ? How will each maiden deal with their powers?
You are just creating more alleged plot points for seemingly no reason. Your original assertion was that there a plot points that need to be finished up. Adding new ones, working from that presumption, is nonsensical. As far as your question relates to Salem, she has no bearing on the Maidens' power. Better question would be what happens when, or if, Ozpin completely disappears, as at least then there is some sort of a connection (the writers have stated that the Maidens are draining his power; he has created them).
What’s the deal with the unacounted maiden? How will she affect the others?
Again, adding plot points that needn't be there. I don't see why she couldn't get the Atlas Maiden treatment; mentioned when important, and soon after killed off. This also has the benefit of aligning with what Cinder wants to do anyway.
Will Raven redeem herself and start fighting against Salem directly? Will team RWBY become maidens, if so what does that imply?
These are not even plot points. These are just questions. By your metric as long as there is an alive female (or a male in a female body as is the case with Penny), the Maiden thing is one big unresolved plot point. That's nonsensical.
As it relates to Raven, that is only relevant if we assume something more in the Maidens then them being glorified keys. Though, to answer you,
they wanted to do that in Vol 9, but cut that out
As for the Faunus You might remeber there is in fact a terrorist organization running around, that they suddenly forgot to deal with?
That's not a racism question, though, and that technically got resolved. The head of the organization was killed (Adam), and their headquarters seized (Blake plotline during Vol 5). Sure there are still probably some elements elsewhere, but White Fang stopped being important after Vol 3 (bar Vol 5). They are just criminals now, and the police can resolve that.
You see by “plot resolution” I don’t mean more exposition or information. We don’t need a montage with still images and a narrator explaining things . I mean actually paying off the plot threads by showing the emotional resolution to them. The latest volume teased to show Summer’s last mission so again that’s another implicit promise they failed to deliver.
What exactly is what you want done here?
What’s missing is the emotional beats of that.
The Farmer spent literally whole of Volume 6 and 7 and parts of 8 coping about the whole thing and talking it over with Ozpin. That's as much as you should realistically get without derailing the entire thing. The best you could ask is maybe an epilogue with some thoughts from Ozpin and a gravestone.
They wrote a lot of checks they can’t possibly cash out with 2 seasons let alone 1.
Sure, I can agree to that