Main Scenario Restriction Bloodstorm - Very Very Bad idea.

[Reynhart]

Yet XI still allowed people to start separate expansion content regardless if they had did the previous or not....

Rhapsodies Of Vana'Diel would like to have a word with you...
You couldn't play ZM without having done the City rank 5. And allowing CoP without ZM is stupid, since it's a direct sequel.

ToAU, WotG and SoA were three unrelated stories, so it made sense...but it still requires max level to do them, so a new player have absolutely no means of jumping right into them.
If they decide to create an expansion where you can start at level one, then yes, gating it behind previous expansions would be stupid.

MMOs do not function the same as games in other genres. Unlike any other Final Fantasy, FFXIV's quest number will only become larger as the years trickle by. It's the equivalent of say, BioWare forcing people to have completed save file of Mass Effect and Mass Effect 2 before they can play Mass Effect 3.

"Wah wah, I can't acces act V in Lords Of Destruction without clearing act IV of Diablo II"
"Wah wah, I can't acces act V in Reaper Of Souls without clearing act IV of Diablo III"