Please Note: Blue Mage, Corsair, (insert other new jobs here) will be restricted to level 50 on release. Over the comming year we will increase the level cap 10 levels at a time.
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This is SE after all. Just think about all the stuff that would have to be in if the level cap was 75 on release:
1: Unlock job quest
40: AF1 quest
50: Subligar, JSE (changes to Aquaducts and Sacrarium)
52-60: AF2, AF3 quest (figure out where to put new af coffers)
70: New Maat fight
71-75: Relic Armor + belt/cape, new Relic Weapon if they add a new class of weapons (so changes to all dynamis zones)
74: AF+1 (changes to limbus zones)
75: Relic+1 (just a change to the no-sj loot tables, and a couple +1's to the relic stats, so relatively easy)
75: Job Specific Merit Categories
That really seems a whole lot of work for SE to do
(and actually almost seems like more new content then all of CoP)