That doesn't even make any sense, first off I want to say that I don't support the idea of "Potions" at all for this type of thing. There are ways they could catch players up by cutting fluff fetch quests in story missions etc.. and increasing level gains in old content by adding a bonus when below a certain level.
There is nothing to this then an extra way to get money. Its a blatant money grab, while shamelessly putting it under a banner of "We actually really care about you guys being able to play together"... my point was, if they actually cared, it wouldn't cost money to do it.
Like don't sit here and talk about how you care about the players playing together while proposing a payable option on top of purchasing a game , on top of paying a monthly subscription cost. That doesn't even make sense. Just say you want to add this thing, don't make it sound like your doing the community a favor.