I don't know much about game development and stuff like that, but even still I don't think that should be a priority. This reminds me of the nuzlocke mode that people want in the games, but I personally don't agree with that and think that it's much better to do stuff at your own pace. Imo there are much more important things to implement and the game has a lot of features that aren't implemented(the trick house, half of Nimbasa...) and although a hard mode could be fun, this may be too extreme and frustrating to the point that you would need to have a competitive team. And if you have a competitive team, it may be better to play in actual competitive.