I see what you are saying, but I can't say I agree with not bundling it with at least one of the potion types. To me adding a price tag on top of purchase, on top of subscription doesn't sit right in the spirit of "catching people up" which is their entire reason on even adding it. By adding it bundled with an expansion, it doesn't benefit anyone that has already finished ARR/HW.(for the story potion anyway) It only benefits people that are behind and only if they want to. Any additional purchases would be for alts etc... Thus making it look less like a money grab, and more of an optional service.
Also you can't use the thing until free trial is over, so if they played they would still need to play through old content, either that or sit on their trial and wait. This gives people time to think ... Do I want to use this thing? If I get to pick one, what do I like more, Grinding story or grinding levels? The people wanting to skip story would then have to make a choice... do I want to now buy a potion to level? and people that got the levels, would then have to ask do I want to buy the story potion?
The additional plus side to this, is any existing player (that is done with story) that wanted to play a different job, that they don't have up to the latest expansions level, would be able to use their free job potion, to jump right into the thing they wanted to try.
I honestly don't like the idea of jumps at all, however; if it was handled like this... I would be less grumpy about the whole ordeal lol.