Like I said in the past Jump Potion thread that was deleted, I think SE wrote/developed themselves into a corner on this one.
New players will have to go through 286 ARR's MS quests and whatever amount HW ends with (we are currently at 94 quests) just to get to Stormblood.
Between doing the quests, leveling, dungeons, trials, and traveling from point A to B, the new expansion will have a huge time-sink as a gate.
This is going to be disheartening to any new player coming in because of what they see Stormblood will have (jobs, story, locations, fights, etc).
I think in the future, SE needs to look into not being so linear with their expansion design and maybe cut some of the fat off of ARR's MSQ, while also upping the amount of EXP you get per each quest, so people can get to 50 doing the MSQ.

Having said that, IF SE introduces a Jump Potion, I think they need to:
A)Make it one per ACCOUNT, not character. This is more to prevent RMTers from abusing these to get to HW and SB areas.
and
B)Have those who use it go through some form of basic training. I think just plopping a new player into a level 60 environment would be to frustrating for both the new player, who wouldn't know what they are doing and wouldn't have the muscle memory down, and veteran players, who would have to teach them.