50/50 is the chance most people get for most things — it’s the standard difficulty. You have a 50/50 chance to pick a lock, bust down a door, shoot most things, etc.
I would have (perhaps an advanced rule) where all unattended items have one skill: Universal 3d6 (10). And the GM can decide some items have higher or lower values for this skills. So you might have a Lock that is Universal 5d6 (17) and thus it is harder to pick with thievery, or break with Fighting.
EDIT: The other benefit of a Universal skill for unattended items is it co-insides with, say, using Magic to create a wall of fire. The wall becomes an unattended item whose dice size is the same as the Magic skill used to create it.
Oh, and you said everything is 50/50. But it isn't 10+ on 3d6 is 58/42. If you wanted 50/50 odds, everything would be 3d6 (11).