Basically what Motenten said, it's probably a way to address the complaints about Ark Angel & MPNMs in general. People right now build up 30 MPs so they can do fights, they do one, maybe do it again, but then they run out and have to go merit some more. With the ability to hold up to 45 Merits we'd be looking at 4 runs at a 15 Merit Point cost fight or 3 runs at a 20 Merit Point cost fight, both increase by 1 and as such it helps address the issue a bit as you won't have to farm Merits as often between runs.