Honestly, I think that it would be too overpowering to have this implemented. It would also make lots of the gear that is difficult to obtain (such as rare drops,turn ins or donation) worthless. Also there are some items that have one property that is really high (such as a 100% life leech) that if you combine a few of these the item would become way too strong. We already have the augment system in the game where we can add 5 sockets to jewelry and armor that can be used to customize gear. I think we should just stick with the augments, maybe there are some augments that could be added but I haven't thought about that.