This is a great idea, but two problems stand out:
1: Experience players and new player don't see eye to eye. Experienced players may take their time to teach the new guys and girls, but a new player may take too much time since they want to loot and look around. Even so, one player could disconnect which could make it harder for the new player to figure out, or the experienced player quitting the current mentor system and look for a new player to help out.
2: Reading the post on facebook and about people's concerns they love the mentor system but the boosting the new player does spoil the content of the world has to offer. Compare both high-level and low-level mentor system, the newbie has no clue what do as they suddenly got all these skills and boosted health and damage. They may feel so powerful that when they go back to being low-level, they will find another high-level mentor and stay like that until that mentor gets off.
It's still a great concept, and I hope to see it work well! My pros:
1: It's a great system for high-level players to teach low-level players, encouraging the low-level players to come back to play more once they get off. Rewards (I suspect that both players will get the same in a dungeon) can be given so they can earn more money while keeping one set of the same equipment.
2: Tactics! Any new player that joined can be taught by a higher-level about tactics that would be needed if they're going to be in a party with other people, raid, or clan to fight for resources. Each person has their own preference of doing their own thing but with other players, they (high-level) can walk through the new players on what suits them best (as long they know what they want to become).