If you are running a custodial wallet and your main objective is Bitcoin adoption and user self-custody, then you are not making your app profitable because people will be leaving your app or using it with less BTC. But I guess it might work, maybe in the long term you will create a good reputation as a simple to use wallet which educate they users with a complete section where explains the keypoints of self-custody. I can imagine an app as simple as wallet of satoshi with a button in the menu with articles about this matter. So it's possible with a good UI.