So, you already radically increased the utility of having mule characters on the same account by letting us transfer previously-untradeable EX items between characters on the same account.
However, the actual process of this is incredibly tedious. Having to run back and forth between mog houses and delivery NPCs, and relogging repeatedly while doing so, is a massive waste of time and almost defeats the purpose of having said convenience.
I'd love to see some additional delivery options added if you're transferring items to a character on the same account. Some off-the-cuff ideas:
1. Add the ability to have a character on the same account auto-accept a delivered item, given that the recipient is both in their mog house and has open space in their current inventory to receive the item. This way, same account muling would not be restricted to transferring 8 items at a time, so big batches of e.g. crafting materials could be shifted much more rapidly.
2. Add a mini-"delivery" option to the Mog House that could only select characters on the same SE Account for delivery. This way at least the re-logging would all be done within the mog house, and would save on loading times significantly
3. A bit more far-fetched, but possibly adding an "account inventory management" system to the title screen prior to logging in would be simply godlike in utility. Having this on a web page would be even better, but could far too easily open up very dangerous security issues so this entire option is probably more wishful thinking than anything else.
Really though SE, we're paying you an extra dollar each for these content IDs. Let's get some more utility out of that extra money we're paying you!