The tablet and smartphone have made handheld consoles a niche product. With competition from Nintendo 3DS/2DS, Sony PS Vita and Nvidia Sheild (Sheild 2 with Tegra K1 chipset is currently rumoured too) at the high end and Pandora/Pyra covering the homebrew/hobby/retro area there's very little room for an Amiga specific handheld console. It would be hideously expensive, underpowered and unsupported by 3rd party developers even if you could put one together.
An FPGA Arcade Replay type handheld with modest 68k softcore performance and slightly improved AGA graphics, LCD screen, battery and a housing with some buttons/joysticks might be technically achievable but doesn't have a market like the actual FPGA Arcade Replay does.
Talking of the Replay and mobile technology a Slimport transmitter IC would make a nice AV output option since you can't have HDMI directly due to the high annual licensing fees.
Suggesting a PPC based 'Amiga' handheld is an even more out there idea than a 68060 based one.
