Oh great... Now I'm going to be watching each update and will be thinking of this now:
So anywho, let's take some more wild guesses.
Chain- A bit weird to see a chain user if Ninjara already had that covered, but I suppose that people could have the same type of arms perhaps. This could be either like a warden, a prisoner, or a bike gang member.
Coil- Byte and Bark come to mind here, but I suppose we could have a character similar to Byte but from a different perspective of a "clockwork" character
Plant- From the people who brought you Helix probably will be same who could have made this monstrosity come to life. Would be neat to see an actual fighting plant with Vine ARMS.
Robo- Don't know if this overlaps with Byte and Bark again, but perhaps this could be less clockwork and more "Robo" so to speak. Still, it would be interesting if we had something similar to Max Brass where he is almost like a "Spring Man 2.0" to where it is like Byte and Bark, but with its own sets of pros and cons. We'll have to wait and see.
Scroll- Don't want to say Ninjara again, but perhaps it could be someone who is the "Wise Old Man." Hell, that could be something close to Minmin perhaps in terms of fighting styles.
Sumo- Definitely an interesting one to consider and pretty straight forward with how this character would be. Perhaps he could have sometime that could be like either having a close ranged special attack unique to him, or something that makes him harder to knock down.
Surprise- Best I can think of is a guest cameo (which there has been alot already mentioned so I won't try and guess since they are all great answers).
Sweet- below.
Twintale- I feel as though mentioning Twintelle would be redundant here... Still, as I said many times before, wouldn't be shocked if there are people who have the same kind of ARMS in the world of ARMS. Doubt it would be another movie star though.
Alot of fun ideas all around for possible characters. It just makes me wonder though how they will be in terms of play style since for some reason, I was doing alot of comparisons to existing fighters (and I don't want to think that we might have cases where they will be a mix of existing fighters as if to give them a slightly higher edge. Then again, I don't really know how Max Brass has ranked in the tier list lately, so who do I know?)
Edit: I forgot about Sweet! You guys know what this means?!
TAFFY IS COMING TO ARMS!
Or if I had to guess, the fighter who is "Sweet" probably will have Taffy ARMS