It is easier to port games and apps from equal systems to 68k amigas than from modern world.
Games from systems in the early 2000s can also be doable. Examples include Game Boy Advance RPGs and strategy games such as the Advance Wars series (GBA and NDS).
Of course you'd have to write everything from scratch, and it's probably best done in assembler on slightly expanded machines (Adnvance Wars 2 can be done properly on an A1200 with just trapdoor fastmem and an internal HD/CF, if I'm not mistaken).
In my opinion, the only impossible things seem to be 3D games, although the Playstation 1 Final Fantasies all use prerendered backgrounds and only use 3D for character/NPCs and the battle screens (and this 3D isn't exactly advanced, maybe doable with some sort of Doom style engine). Characters/NPCs at locations could be done by partially pre-rendering them (most of this stuff can be easily ripped using modding tools) and using old style point and click scaling.