IMO if there are levels you should be able to choose practical abilities. see better in the darkness, hold your breath a bit longer, a little more health, better accuracy with the bow, quicker digging, more weapon damage, and so on. that would add a bit more strategy to the game and would allow you to create custom classes, if someone had higher health, more weapon damage, and more time underwater they could easily defeat someone who had quicker digging, a bit more health, see better in darkness, and quicker digging. though the person who had the better combat levels would rely on the miner for supplies. this would also give more depth to team work. currently mining groups are just a bunch of people with pickaxes, with this they could be a group of designated miners and guards, who can defend them from mobs that spawn in tunnles. it would also go good in pvp servers, better teamwork would all be achieved by having archers and swordsmen, archers would have better accuracy and the swordsmen would have better weapon damage.
I'm saying: of all the things you could pick from adventure games, you pick the one that encourages grinding the most.
Goblin villages? No. Cool weapons? Nope. Dragons? Hell no.
We want LEVELS!11
I only hope that they won't be like "get level 10 to be able to mine iron!"
And that they would be more like "you have used a bow 200 times, your range is now increased by 20%."
both of those are terrible considering you need iron to survive and you can fire off three stacks of arrows in less than a minute.
also, isn't minecraft already grinding? considering you need to get supplies for your house. what difference does it make if you have some levels there too, you'll still be digging, you would just have perks. either way, the levels are gained through orbs, that means that there is no grinding, only exploring.