It might be a good idea to start thinking about how this will play out before the game officially launches. If skill gain is solely achieved through repeating the same action, this will inevitably lead to rampant macroing. Just look at DF and where they are now. The game started with heavy exploitation of mobs for gold and resources which were then used to nonstop macro skills to the highest levels in a very short amount of time. The devs never saw it coming.
The way I propose to combat this is through an Eve Online type skill gain system to complement the other system. So you can put a skill you want raised in the queue and that skill will lvl up to X in Y amount of time. That skill will then be locked from gain the normal way so you can't get double gains.
This would allow more casual players a way to keep up and also give more control over character progression timeline to the devs. That is, if the afk/queue system was more efficient than the repetition system.
Edit: this would also allow for more sandbox type play as you wouldn't feel the need to grind skills while in game.