First of all, the coding effort is large.
Second, it would be a large stack of possible "got a revenge open"
Thirdly, as this would circumvent the limits, it would get unbalanced.
Fourth, an alt (avoiding the current anti-alt-pvp module) would attack the main, get up, and the main attacks him, smacking off his xp. the best would be to have a sitter char at level 15
grabbing tons of xp at chuunin level, you be master hokage. let him attack you, you kill him in revenge and get xp. if you remove the xp, then maybe.
Fifth, the "take revenge" cannot be done from the mail. the mail cannot be interactive, coding wise. (everything can be done, but I would turn everything upside down.... which would be a point to start now program my own game engine, and make around 2010 or 2011 the first run with this engine.
1:11am, and my head is empty.