Is it possible to reprogram an Arduino wirelessly by using Nordic Semiconductor's nRF24L01+ or nRF51822? Thanks!
The nRF24L01P appears to communicate via SPI. The following article may be of interest: https://wirejungle.wordpress.com/2010/08/16/programming-arduino-with-arduino/
Yes, it does use SPI. Is the RF device, though, going to be able to communicate quickly enough to reprogram the ATMega328P?
It's hard to say for certain, The speed will probably depend on the clock speed of your Arduino. The RF module appears to be fast enough, though I have not used any RF modules in my designs thus far.
Another issue to overcome will be resetting the Arduino prior to programming.