I find it interesting, from the novelty side at least. I am still worried about the lack of real peripherals, what happens when I want 16 peripherals? I haven't counted, but for a sizeable project that must be a limit. Having said that, I would quite like a dedicated "stepper driver peripheral".
Parallax do an Arduino format board for their current Propeller chip, I guess they would do one for their Propeller 2 chip. So maybe the hardware side is already covered, although I think the hardware is the easy bit.
The hard bit I think would be fitting the Propeller architecture into Arduino IDE. I guess that the IDE can launch a compiler and download to unusual devices fairly easily, but a lot of what people mean by Arduino ease of use is in the libraries - serial, io, analog, wire, spi etc. I guess those all require a complete rewrite for Propeller, which could be a big job.
I see that Parallax also have an IDE, I guess it can download as well. That kinda raises the question, why not use the Propeller IDE for programming it?