Successfully built the library for Win IoT 10 Core. Most of the conversion was straightforward (things like converting "Ticks()" to System.Environment.TickCout; converting the Thread-ing calls were a little more work, but not much...). I'll start testing tonight or tomorrow.
There's one material change. Win IoT Core doesn't have an InterruptPort class nor InterruptPort's DisableInterrupt()/EnableInterrupt() members. You can instantiate a Gpio pin in Win IoT, set the pin's DriveMode to Input (InputPullHigh in this case/if the pin supports it), and attach a handler to the pin's ValueChanged event which is nearly the same as attaching to an InterruptPort's OnInterrupt event. In the ValueChanged handler, you can determine if the pin's Edge is falling or rising (I think we're interested RisingEdge in the RFM69 class). But I think the Gpio "interrupt" pin could still receive input while the ValueChanged handler is executing. I'll take any guidance anyone cares to offer about handling interrupts properly in Win IoT.
Similar issue with OutputPort; there's no OutputPort class in Win IoT, but you can configure a Gpio port as output, set the initial state to false (Low), etc. So I think the reset pin will work just fine.
A few other async/threading related-clean ups, but I'm hopeful I'll have something to share in a few more days.