Heavensward new jobs information from PAX East

Dark Knight:

* Involves more MP management than with the existing tank jobs

* The job uses MP to cast darkness auras that can either have offensive or defensive capabilities such as damage/defense buffs or AoE damage

* Switching between the auras while managing MP is a big part of the new job

* Sacrificing one's HP may be a mechanic but it is not the focus of the job

Astrologist:

* The job has two stances, "heal" and "barrier" (tentatively named "moon reader" and "star reader")

* Switching between the stances involves a delay since they're quite strong

* Spells remain the same but their effects will change depending on the stance

* The astrologist draws cards to buff the party, there is a random element to which card you get

* You may use the card immediately or save it to be used together with another card

* Thinking fast on your feet is a big part of the job; there is a high initial learning curve

Machinist:

* Ranged DPS with strong support capabilities akin to Bard

* Involves managing attachments to support yourself and the allies and turrets to debuff the enemy

* Using attachments on your rifle will turn it into a cannon. There will be a charging effect and the longer you charge the more powerful the attack will be. Moving resets the charge

* Gun actions require a stacking ammo buff. Learning when to reload will be an important skill

* Managing the cannon and the placement of turrets for maximum efficiency is the primary mechanic of the job

* Hitting different parts of the enemy will also be some sort of a mechanic for the job

Sources:

http://www.siliconera.com/2015/03/13/final-fantasy-xiv-director-explains-heavenswards-new-jobs-planned-au-ra/

http://www.reddit.com/r/ffxiv/comments/2z06p9/famitsu_paxeast_interview/

It seems Machinist will be like a mix of Black Mage and Bard. BLM in the sense that you'll have to determine when to stop to do actions and when to move around without sacrificing DPS, BRD in the sense that you can support your party.

Astrologist probably has quite a high potency ceiling in comparison to SCH & WHM to make up for the random element and the stance limitations.

Dark Knight may have better offensive burst capabilities than WAR and PLD depending on how well the player can read the encounter.