Ironically the Gameduino seems to pretty much emulate roughly the capabilities of a Propeller. (Even down to having 32k of RAM. Granted there's probably somewhat more actually available on this for tiles and sprites, since the Prop will be using at least some HUB RAM for the video and sound generation software.)
Still, I can see the attraction. One feature the Propeller could really benefit from is a hardware "SPI slave mode". It's possible to make it be one in software but the Prop is better at generating clocks than following them. (For that matter, it'd be nice if it were somewhat easier to make it follow an external clock for parallel transfers, so it'd be easier to use in place of things like 6522s.) That'd make it easier to use as a coprocessor in more "conventional" computer designs where the Prop doesn't run the whole show.
Still, I can see the attraction. One feature the Propeller could really benefit from is a hardware "SPI slave mode". It's possible to make it be one in software but the Prop is better at generating clocks than following them. (For that matter, it'd be nice if it were somewhat easier to make it follow an external clock for parallel transfers, so it'd be easier to use in place of things like 6522s.) That'd make it easier to use as a coprocessor in more "conventional" computer designs where the Prop doesn't run the whole show.