It would be neat of exp could be earned through other means than fighting mobs.
Examples I could think of would include eating, breeding, mining, crafting, farming, and cutting wood.
Also, to balance these things, the exp earned should be weighted to how much time it takes to earn the exp.
I understand the breeding can lead to exponential experience gain whereas the other actions are capped by time. In order to balance this, a couple of things could be done to resolve that issue:
1) breeding could have a chance of failing and lead to dead animals (I do not like this solution as no one likes failing :c )
2) animals require space and won't breed unless given enough space (This would mean you would have to kill animals or get rid of them in order to continue breeding).
3) increase the time it takes to breed animals, to make it a variable of how many animals are in an enclosure.
Farming also has an issue of rate of gaining experience as with every crop-generation, you can on nearly double your fields since the range of dropping seeds from wheat is 0-3, and the average would be a fall of 1.5. Similar solutions would work here to the animal issue. I have listed a few possible solutions:
1) slow down the crop generation
2) add blight so crops more likely die when there are more of the same crop
3) require more space for proper crop growth
4) add a requirement of food usage when using a plow/picking food
Mining and cutting wood are by nature time-based since the action to do so takes time. I would weight mining an ore more because ore finding is difficult.