A long time ago, I used to play in a heavily modified CircleMUD that had one of the more entertaining character growth situations I've seen. The core of the game started with rules and a world based in 2nd Edition Dungeons and Dragons, but diverged dramatically for gameplay purposes - a level cap of 49 versus the usual Dungeons and Dragons caps, for one thing. Without going too far into detail, the game had close to a dozen unique character classes and way, way more content than was practical for any character to experience at all level ranges, even extending beyond what was realistically survivable for a single character. Rather than having players roll a bunch of characters, their solution was to create a mechanical and storyline justification for the characters to experience more content across all levels.
Once a character hit level 49, they would find out about a unique quest via word of mouth or a few very limited in-game references to a process called "Remortalization." In order to perform this, the character needed enough experience to reach an equivalent level 50, and a significant amount of in-game currency. Once the character had this, they had to track down an NPC somewhere in the game's far corners - it spawned randomly and frequently moved - get to it, and defeat it. That goal finished, the NPC dropped a "Skein of Fate" the character would enter, and then be faced with a literal 10-question quiz about the area of the game world that is presumed to be usable for their relative level of power. If they passed this quiz, they would have their character reset to level 1. There were a few perks, though, that made this highly sought-after.
The most blatant perk to this was, upon remortalization, the character would be able to pick a second class. This was not a watered down second class - it was the full-featured, all skills and abilities accessible as-if-you-picked-it-first class. This allowed characters to explore the combination between their initial class and any of the several other classes in the game. The character could change their secondary class each time they completed this process - I know I personally tried Cleric/Mercenary, Cleric/Psychic, and Cleric/Physic on the same character. Some class abilities also only unlocked after remortalizing a certain number of times. Also, characters received a modest increase to the natural numeric caps that existed in the game. As per 2nd Edition Dungeons and Dragons, the Human was limited to an 18 in any given ability score, with other races having their racial modifications adjust the ability cap accordingly. A remortalized character would, upon their "rebirth," increase all of those caps by 1, and have a modest increase to the caps of some behind-the-code numbers. On top of this, the "new" character would (with the foresight to hand off their gear to a trusted friend, or leave it somewhere secure that they trusted) have all of their high level equipment. The one downside to all of this was that experience gain was not quite reset - the more powerful character had to work harder to gain their experience towards their next level. Each time a character remortalized, the numbers went up and the experience got harder. On top of that, the cost of the next remortalization went up considerably. Remortalization capped at 10 iterations, and characters at that capstone were somewhat rare.
The net result of this was that the in-game content was much broader in scope - some "low level" content would actually be designed to be harder and more rewarding to the remortalized characters versus newer characters, and there was a great deal of top-level content that would be far too hard without the numbers cap increase. Between that was a vast amount of content that was usable by characters across the scope of levels and "generation."
So... how would something like this look in Alliance? I've got a bit of an idea after reading this thread and remembering that old game, but it's pretty half-formed and has problems to address. For instance, we don't use a hard-class system, so the reward of a secondary class wouldn't work. There are also not so many "behind the screen" mechanics that could be manipulated. There is also the problem of magic item creep, which can dramatically skew a character's relative power.