Simple concept: take the shared guild bank concept implemented in many MMOs today and apply it not just to items, but to characters as well.
Group content and group play requires, well, groups. To experience much of the group content and endgame content (at least in WoW) you will need a group that shows up, is well balanced and well geared. Most MMOs suffer from any number of barriers to grouping and as a result, much grouping (and acquisition of grouping skills) doesn’t happen until the endgame and even then still suffers from class population imbalances.
Even when you do have a good group of folks dedicated to mutual support and group play (aka a Guild), class population imbalances and level disparities within the guild can still mean barriers to group play. Judging by what I read in MMOG blogs and the LFGs in game, holy priests and protection warriors are a fairly rare commodity at the level cap in WoW. One reason is that these two classes in particular are more difficult to progress solo. Talent respeccing only goes so far because lets face it, a good tank is a lot more than just a L70 warrior in welfare epics with a bunch of talent points dumped into protection and it gets expensive to flip back and forth from fury to protection.
Enter the Guild Character (aka Rent-a-Toon). Players create characters and progress them through the world in the ordinary fashion. If they join a guild however, they can designate one or more of their characters as “guild characters” which can be played by any member of the guild which has permission to do so. Essentially, when you log in you could choose to play one of your own characters or a guild character (if its not being played by someone else).
All the experience would accrue only to the guild character and there would likely need to be some lockouts on selling bound gear, etc. so that only a guild officer or the owner could choose to sell off or DE gear. Any items acquired by the shared character would be freely transferable just like stuff in guild bank slots and gold acquired while played as a shared character could be only contributed to the overall guild bank.
Lower and higher level guild members could now actually play together and contribute to the collective effort. What a great opportunity to mentor younger players, “hey kid, we need a fifth or tenth for instance X, go grab a L70 guild character and join us for a crawl.”
Keep a few protection warriors in stock and the entire guild could focus their efforts on getting one MT fully geared or when that group of 5 hunters shows up, a couple of them could sub in as a tank and healer. It doesn’t completely solve the “I can’t get a group to finish my hunter’s x quest” but it sure increases the chances if any number of guildies could hop into a shared character to assist another guildy with a balanced group.
Lots of antiexploit, antigriefing details to consider (like whether the character would stay if the owner left the guild), but this would actually foster more group play, help alleviate class population imbalances and allow people to learn to play a different class.
Thoughts? Let the flogging begin.