I assume that the RX 460 MSI card that you have is a 4 gb version. 10 MH/s seems very good - I have seen people getting it to 13 MH/s, but this could cause a lot of GPU Memory errors, which is not good.

Well, difficulty could also rise the price of an ethereum, but yeah, when people stop mining ethereum because their hashrates drop, then we will see another coin go up, and the difficulty of ethereum would decrease aswell, which could lead to somewhere near this profit, that we are earning today, but who knows.