Pay for your inventory.

[FriendlyUncle]

The developers said the inventory limit was a speed/safety issue. If they increase the inventory then they can only sync it to disk half as much, which means if a server crashes, you "roll back" and get a lot more customer service complaints.

In older games, "stacks" were simply represented as a quantity variable. Hence "dupe'ing" bugs, especially gold dupe bugs were prevalent in pretty much every MMO at some point. Newer games actually account for all the gold and items on the servers, at the cost of intended inventory space being reduced, and the glamour systems require the game to keep track of two items, not just one.

More to the point though, almost nobody has ever played a game where the inventory space was nearly unlimited and lived to tell about it. Everyone finds a way to work around the space limitations, even if it involves making it an extreme pain in the ass.

Because:
1) Every item requires being sent across the wire. FFXIV is so responsive because there are so few items being sent. Even not-so-old (freemium) games that let you buy expansion slots, were never this fast.
2) Searching inventory and market boards are fast (market boards occasionally time out), and searches check your Retainers.

This one time, in this one other MMORPG game, I lost my dress that I had worked so hard to get and dye the right colors... and lost it to a server crash because I had just changed gear. I will never forget that.

This might have been a valid excuse 15 years ago, but with the increase of HDD space and read/write speeds, no this is not a valid point. Servers will not be taxed by adding 1-2 more inventory tabs as compared to adding 4 additional retainers that can store 1300 additional items, has its own character model, equips its own set of gear which also has to be loaded into the game, also has to keep track of the items each of them have listed on the MB. Even just 1 additional retainer fully decked would cause more of a strain on the server than adding normal inventory slots to the player character. The fact that they added the option to buy two more retainers and then just increased it to six is just proof that SE doesn't even believe that piss-poor excuse.

Inventory storage is just a database. Adding a few more lines referencing items will not cause a noticeable degradation of performance unless they are re-using old FFXI servers from back in '98. In which case they need to upgrade their hardware. The amount of data that makes up a single slot of inventory is minuscule and the responsiveness or lack there of has nothing to do with inventory data. I'd be willing to bet just your character model and position is more data sent across to the servers than having your entire player inventory completely full, max inventory stacks.

SE is willing to add additional retainers whose inventory as far as I'm away is essentially exactly like the players data usage wise and inherently uses additional data than standard inventory because Character model, equipment, venture status, items on market, gil counts vs player inventory which just holds items. This very fact proves that SE does not think additional inventory checks will tax their back-end, rather they used an issue for some and came up with a way to try and nickle and dime sub paying players for additional inventory and monthly at that. Reduce extra retainers to 6, 3 hired in game and 3 by additional costs, increase armory slots by 3 each to accommodate the new classes, add 1 additional inventory tab to the players inventory and FFS let armor 'sets' be stored in the armoire. AF, AF2, Sets like Allagan, HA, DW. Armoire data is not called during inventory checks. Clean up the clunky glamour system to obtain item, get glamour. Crafters still get people buying their items for glamour, players don't have to cling onto the same piece in case they want to use it again or sell it and risk having to purchase it again later.