Of course it will be a step back, I'm really used to touch control my handled now. When you have a DS game without touch driven menus, it seems really old...
The only thing that could be improved is the removal of this second screen. Really, there's no use to it. I'd rather like a bigger screen and a more compact design.
If you think I'm wrong gimme names of games where the dual screen is really useful, and I don't mean things like maps, because ok it's convenient, but if you look deeply, I'm not lost in gba castlevania where I'm two buttons away from the map. Also, second screen only for game control is a mess, for every game having their control on the second screen (Super Mario 64, Metroid, ect...) it was better with classic controls.