Although Adafruit Feather 32u4 and other ATmega32xx based boards are (due to limited memory) much less suited for new LMIC based LoRaWAN applications, the statement “adafruit 32u4 feather does not have enough RAM to run the LMIC software” is not correct however.
The MCCI LMIC library will run just fine on ATmega32xx based boards like Arduino Pro Mini, Adafruit Feather 32u4 and BSFrance 32u4 II. The only problem is that there will not be much room left for larger, more advanced sketches due to the (nowadays) limited memory resources on these 8-bit controllers.
Over time LoRaWAN versions have changed, new features have to be supported and the memory footprint of MCCI LMIC has grown accordingly. For this reason the LMIC-node example application cannot use MCCI LMIC with these boards. The ttn-otaa.ino example included with the library will run fine however.
As @terrillmoore already mentioned: to use MCCI LMIC with these 8-bit controllers it is best to disable Ping and Beacons to minimize the memory footprint. It is also necessary to relax LMIC timing by setting LMIC ClockError, otherwise downlinks and OTAA joins will commonly fail with these boards.
For setting LMIC ClockError see here and here for an example.
LMIC-node does not (directly) support the Adafruit Feather 32u4 (because support for this board was not yet added). LMIC-node does support some other ATmega32xx based boards however.
Due to the ATmega32xx’s memory limitations, LMIC-node cannot run in combination with MCCI LMIC (preferred) on these 8-bit boards. Instead it will use the Classic LMIC library for these boards which is smaller. Classic LMIC is deprecated however and (much) less LoRaWAN compliant which is/can be an issue for TTN/TTS V3.