The tertiary firmware for WL1271/3 supports RFMON just fine. The driver, however, does not. Same as with the WL1251 chip.

802.11 "promiscuous" mode is not referred to as 'promiscuous mode' per se. It is RFMON or "monitor mode" where a card is adjusted to passively Rx any data on a specified frequency. This is a function of the firmware that is normally disabled in drivers.

Monitor mode is present in the stock driver that ships on the N950, it is slightly broken and the upper stack does not support it. mac80211 needs to be backported and a patch to allow proper RFMON and live-frame transmitting without association (aka packet injection) is required as well.

Of course, the 1251 and 1271/3 drivers are inherently similar, and as the above poster noted, they are completely open source. Once aegis-free (unsigned) kernels can be flashed and are fully functional, development for this can take place.

Until basement-brew is possible on the N950 (which is a decent way off), this won't be and unless we can raise some funds to get this done, I suspect it won't ever be.