That's going to work great ...  Until one or more of the coins they are staking gets dumped and they get left holding the bag. Or when one of the coins they are staking gets dumped and the owner can pocket a bunch of bitcoins by claiming to have lost more in that dump than he really did due to the lack of transparency.

That idea would be ok if they collected various coins, staked them, and paid out the profits in the same coin. That way the users would have the level of risk for each coin that they choose, giving them bitcoins and allowing them to "diversify" them into various coins means that it really boils down to you sending him coins and letting him trade them for you. The staking gives some sort of backup plan, but that business model has a long history of failure, and way too many points of failure and/or ways to make a scam look like a failure.