Seems to me that implementing rewards upon reaching certain amounts of achievement points (500, 1000, 2000, 3000, etc) would be a fine motivator to get people to delve into all aspects of the game.
Like myself, I don't do PVP or fishing and got basically 0 achievement points from those areas. However, if significant rewards for achievement point thresholds were obtained (maybe bonus skillpoints or small increase to health, stam and magicka or level appropriate gear) then maybe I would put the time into the parts of the game that I wouldn't otherwise bother with.
Thoughts?
V14 Templar Argonian Healer, V12 DK Orc Tank, V2 Sorcerer High Elf DPS, V1 Templar Breton DPS, V1 Nightblade Bosmer DPS, and 3 low levels.
Check out my ESO journal["
http://forums.elderscrollsonline.com/discussion/66004/kuratla-s-eso-journal"]