This is going to be the motherlode of patches. The make it or break it patch. The 1 year anniversary patch. The "how the game should of released" patch. This is the one that either wins everyone back or spirals the game into oblivion. It all ends here. Maybe that's a bit dramatic, but yeah, this is the big one.
A "quick" summary I quickly typed up scrolling down for the people at work or too lazy to click the link:
Patch 1.19. "End of September":- Chocobos added. Rentable chocobos AND company-issued personal callable chocobos. Tongue-in-cheek called the "My Little Chocobo" system for now.
- Airships added. Links the cities together, pay gil and hop aboard.
- Ifrit battle. R30 and R50 versions.
- Beastman stronghold raids. Not entirely sure what this is.
- Low level "public" dungeon for low level players. Again, not entirely sure what this is.
- Treasure chests found randomly in the field outside of quests/leves.
- Uncollected guildleves can be stacked as tickets and done all in one go. Allows players to save them up and do lots of them all in one go at the weekend.
- Damage algorithm revamped. No more rank vs rank nonsense. Gear will finally matter!
- Physical levels abolished. Rank renamed to Level, skill to EXP.
- Stat progression is now static and linked to your class and level, like it worked in FFXI (and every other MMO). In Patch 1.20 the ability to customize those stats will be re-introduced and you'll be able to customize your stats *per class*.
- New claiming and linking system.
- Enemies will "call for backup" if you're stronger than the enemy you're fighting. You'll also gain experience bonuses for fighting links.
- The new claiming and linking system will break battle regimens. And rather than delay the patch, battle regimens will be disabled. Battle regimens will then be fixed/overhauled and reintroduced in patch 1.20.
- Experience Chains.
- Crafting recipes will be simplified. Old recipes will still work for a while and then eventually be scrapped. While this isn't mentioned, it sounds like they intend to get rid of the "make sleeves, then make a front, then make a back, and then finally make an item" stuff.
- Materia System. For people who don't know what this is, this is basically enchanting weapons and armor. Equipment you use accumilates points and when they hit max can be converted into Materia that can then be added onto a different weapon. eg: Convert your sword into a STR+5 and then attach it onto a new sword.
- Gathering classes getting sneak/invisible/stealth type abilities.
- Lots of various UI stuff. Too much to mention but it's mostly new to accompany all the new stuff.
Patch 1.20 will be the big class/job balance patch that moves all the abilities around and stuff. Apparently their balance intentions will be posted around the time of Patch 1.19, which will give players time to give feedback on the changes (ie: cry about it) before they are actually implemented for 1.20.
EDIT: Added a few missed important things like the stat progression. The producer letter is definately worth a read if you can open it.