It might be a silly idea but I'm planning to make a FLiPPropStick-like Propeller board just for fun.
If using some kind of USB peripheral controller as a USB-UART interface, instead of FT232R for example, it is only needed less components, i.e. 1 Propeller, 1 UART, 1 LDO, and rest of some resisters and caps. It looks very simple to me.
USB peripheral controller can emulate not only UART interfaces but also I2C EEPROMs, I/O expanders, clock pulse generators, and so on.
In my current plan I'm going to use Cypress enCoRe III CY7C64215 as those 'virtual' components.
Unfortunately CY7C64215 has only 16Ki bytes of internal flash ROM, so it can only hold rather small code for Propeller.