William Does it make sense to use a FQP47P06 PMOS
Not without accurate circuitry to precisely control it. The problem with the configuration you suggest is that this doesn't detect reverse current flow. It is only reverse connection protection, so it won't protect against the case when USB power is 5.1V and power supply power is 5V, where you could sink enough current at a small reverse voltage drop to activate USB overcurrent protection. Depending on the hardware configuration in the host computer sometimes this shuts down all of USB, and in some cases (curse Windows) requires a reboot or wading deep into system control stuff to reset the USB controller and get USB devices to work again.
I wouldn't think 200mV drop as being a real big deal, but if you really want to go for the high precision stuff, look at one of these with an N FET:
It works by modulating the FET at a 30mV forward drop. When the bus supply gets nearly equal to the upstream supply voltage it shuts off and lets whatever is feeding the bus take the load. This shut-off occurs in less than 500ns.
Other vendors make similar devices, but the LT/analog is the most sure-fire for preventing backflow current when sharing a bus, but I think TI has some eFuse products with the integrated FET that do pretty well -- you just have to look closely at these because some use a negative threshold for preventing backflow current and they can sometimes sink as much as several amps before they detect it and shut down the device.