Agreeing that it is too early to say that RMMV is going to make ARC obsolete. However, it does seem extremely promising with all of the features we know of so far; it would be difficult for ARC to compete with the RM-dedicated fanbase. Even if we were to complete ARC, I honestly don't think it will ever reach the levels of immense popularity that it will draw the attentions of users far and wide to rediscover the CP forums, especially when we're giving them a "souped up" version of RMXP (which we have seen a steady decline of; it would be difficult to convince them to come back to XP after having used VX/A).
The only real thing going for ARC, in my opinion, is the engine itself. I do have XPA to serve as my replacement for better performance, but ARC's implementation is probably significantly better. I would be completely happy just having the engine complete and being able to convert my RMXP project to use ARC's engine.
As for the editor, it's not my "child" so to speak (I was invited to the project years after the start of ARC's development), so there's very little sentimental value for me in there. My willingness to join was to help out with menial tasks so that the important big chunks could be handled by Ryex. I need a task list--some kind of direction and steps to perform--if I ever want to get things done. Just looking at the editor as a whole is like staring at the frame of a house without a blueprint and being asked to finish it. I don't even know where to begin.
All in all, ARC lost the momentum and the opportunity to strike fire among the RM fanbase. Its total completion will, at best, give small nods towards our direction.