There are so many suggestions here, and some very very good. I understand that having mine actually considered is slim to none, but I think it's a good idea and would add a new edge to the game. So, here goes.
A PVP bounty system. Something like (of course, everything can be tweaked) 5 random names every few days or week, according to level (something like BG lv distribution). These names would appear in your mailbox and if you found them in the wilds or in the arena, and beat them, then you would get a small bonus. I also understand that some people would/could get very upset about this, so as an option, to take away the 'rage' factor of other players getting hunted, you could simply have this benefit the person doing the hunting, with no harm done to the hunted. A small bonus for finding your marks.
Also, one other small idea. A new shop item. What about a seed protect item? If you get a great seed, and don't want anyone stealing it, would be nice to have a token to place on a single plant.
Thanks for listening guys! The game is fun and entertaining as is, it's just always exciting to see new things! Keep up the good work!