Well, you see? Someone has noticed your post, you've got 10 merits in one shot and now you are fit to become a Member in no time, as soon as your activity is 60. I think this system could work for low ranking members, but only for them. When you join the forum it will take you two months or so to achieve the activity necessary to become a Member. In these two months you just need to get 10 merits - which should not be impossible, or even difficult, for someone who makes decent posts.
The problem rises afterwards, when you need hundreds of merits to climb further in rank. My guess is that that will be an impossible mission, given the scarcity of sMerits. In the rules will stay like this on the long run it will thus become a Forum of Members only - with a little elite of people with higher and mostly frozen ranks.
Well, you have a point of course and perhaps getting the necessary number of Merits for each rank isn't all too difficult (though I think it gets more difficult the higher rank you go).
I think the original intention of the Activity system is to reward active members who contribute to the forum, and assign a ranking for them. It is an own-merit system (my own unofficial term), meaning you yourself control the destiny of your rank. It has its flaws of course, as is the reason for now introducing an additional Merit system.
The only concern I was pointing out on the Merit system is that it is a subjective system dependent on others (and not an own-merit system). This means, you are dependent on not only getting recognized by others but also being favored by them to hand out merits to you. It's a system of chance, depending on whether someone notices your post.
All things said, this just represents my initial impression. Perhaps I could be amplifying the picture or perhaps I could have misunderstood the system, and my concerns may be unfounded. Time will tell how this unfolds.