After so long, I only felt like logging in for raids. I was in a casual raid guild, and we only raided 3 nights a week, so it wasn't hard for me to avoid the game otherwise. Once I started playing on my laptop, I was even able to play my 360 while raiding which made it even less demanding.

IMO, the possibility of that happening really depends on what you mean by "goal-oriented". If your goals include "having the best gear available in the game" or "getting 50 bajillion achievement points", I don't think either of these things is possible without spending large amounts of time playing. If your goals are more along the lines of "play to be best of my ability", "min-max my gear within what's available to me", "choose achievements that are accessible to me", etc., it's quite doable. I also think it depends on how much "free" time you have that you would consider reasonably spent playing WoW. If you formerly played 30 hours a week, cutting down to 5 would be a big drop, but you can still do a lot of stuff in WoW in 5 hours a week. If you only have one hour to spend per week, WoW really wasn't designed for you so that's going to be much more limiting.

I think the hardest part is that you have to change how you play the game, and in a lot of cases who you play the game with. You have to revise your expectations about gear (you simply won't have best in slot drop gear), and if you're a former raider in a raiding guild, you have to keep a firm stance on not returning to a regular raid schedule. I consider myself very lucky to be part of a good guild that lets me raid the casual/alt/10 man/whatever runs whenever I want, and into the main raid whenever they could use me. It allows me to play with my friends (the main point of the game to me) and see most if not all of the content in the game. Really the only downside is that there are times when I log on and everyone is busy with a serious business raid, but it's easy enough to knock out a few quests, PUG, clean the house, go out, etc. Unfortunately, I suspect this isn't true for a lot of people who decide they don't want to "OMGRAID" anymore, since some guilds don't have a "friend" status or like to keep as small of a roster as possible.