When I say this do I mean should Moash get a redemption arch? No, not in the way that you're thinking. I do feel that Moash is beginning to lose what makes him a compelling bad guy. Many understandably hate him for what he has done but I feel that the things he has done most recently have begun to be less captivating(I'll explain what I mean in a minute). So, my question remains, could he be redeemed and become a more compelling character.
My explanation why he is less compelling. In WoR when he conspires against Elhokar there is the belief from his perspective that he is doing something that will bring revenge to his grandparents but also borders on helpful (The example of a surgeon removing the infected part of the body is a good example to me). It may not be the best decision, but it's comprehendable there is an argument as to why it could be helpful. Current Moash seems like a much simpler person. "Give my pain to Odium and get a big bad guy sticker stuck on my head." He'll kill people cause he can, but why? I don't think that Odium's influence is a good enough excuse. I get the feeling that he's on the same path as Amaram, who started out super compelling but became a simple man and was killed off. It just left me wanting and I don't want it to happen again.
When I think of what Moash is missing a couple of classic villain's come to mind. Thanos/Killmonger/(even Todium) all had a purpose that they were working towards albeit a bit extreme but in thier minds is for the greater good. The greater good can be debated, but that's what makes them compelling. Right now Moash feels like a Valda/Joker type person who just does bad things. You bring them up and it's a consensus that, "Yeah, they suck". I know there is a Moash did nothing wrong crowd but unless Moash gets a bit of a 'redemption' arch in a way that makes his character more compelling he seems to be fading away into a sunset of badness.
As for me, I do believe that Moash is redeemable. I listened to the most recent "Intentionally Blank" podcast episode where Brandon and Dan discuss the Wheel of Time and Brandon mentions a couple of things he would have done in the last episodes. They're great ideas, our man still has it. [Wheel of Time spoilers.. kinda]
. So, as for me and my belief... I think he can do it, my fingers are crossed that it happens.