Oh well. Time to earn some hatred for myself.
It would be a huge win for me. Gigantic.
I have two main characters, my avatar and her sister, each on a different account. I play them 99% of the time. I have 6 others, mostly to keep my Guild at six, but I rarely play them. I refuse to create any more characters because of the tremendous time investment to make a decent character in this game. My avatar cannot perform well in Reaper Difficulty so I do not play that at all. I have no desire to destroy my avatar or her sister so I replay Epic Quests over and over and over. It works for me.
Now, you are probably thinking, "Annex, you nitwit, if you only have one character on each of your accounts. Account wide anything gains you nothing!".
If I could earn Reaper Experience playing another character I would immediately create a brand new healer, equip her as best I may, and send her to join the Reaper 1 groups I see. Since all her Reaper Experience would go to my avatar, my avatar would constantly gain power while remaining a cat burglar, happily permanently borrowing stuff while she remains at Epic levels doing her thing.
Shared Past Life Feats would be even more awesome. At L20 my hypothetical cleric would retire and write her magically enchanted Memoirs of a Beautiful Healer in Distress. For game purposes she would be deleted, but her memories would live on as my avatar reads that book and gains the high points of the cleric's life in the form of a Past Life Feat. Oh my goodness that would be so awesome. Robots. Dwarfs. Half-orcs. Warlocks. All the things I despise channeled to my avatar while she remains at Epic Levels as a cat burglar. That would be so much fun!
It would completely change how I play. Someone in the Harbor needs some help? No problem! I will roll up a new L4 character and play with you! I will play with you all the way to L20 if you like! Need a healer for your Reaper group? No problem! Need a robot? I hate robots but, heck, no problem! All the things I hate? No problem! All the things I cannot spare time for under the current system because it pulls time away from my avatar and her sister? No problem! Make 'em, play 'em, write a book, retire 'em. My avatar would be so well read!
*sighs* It will never happen.