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Another update, which is currently under consideration, would allow players to expand the interior size of their estate; for example, a Small estate could have a Large-size interior. This change too, would hopefully allow players to enjoy decorating their estates more freely. In our current concept, expanding the interior will require gil. We do not have an implementation schedule for this feature yet, so please look forward to hearing about our progress in the future.
Finally, as we’ve previously announced, we are currently working to increase the maximum number of furnishings that can be placed in an estate. We expect it to be ready by Patch 7.2 or 7.3, so please look forward to it!
So we know it's coming. To the best of my knowledge, though, they never specifically stated it was going to be doubled. That was speculation on the part of players.