The PSP and Vita were already steps towards the Switch in a sense ("powerful handheld" meaning suddenly PS2-level games were available portably), and the Switch kind of pushing the limits of what people accept as portable devices means that there's almost no market pressure to go back to a small thing. But when you hold a 3DS and realize how easy it is on the move, it makes me wistful.
I would mention the Game Boy Micro as well but that thing is not meant for anyone over the age of 30.