While I couldn't find it explicitly mentioned in any documentation, it appears that the MKL27 sub-family doesn't support USB remote wakeup (driving the D lines to K state). Looking in the MKL27 reference manual, bits 2-4 of USBx_CTL are just marked as Reserved and read-only, whereas for all other parts in the MKL2 series (MKL24, MKL25, MKL26) bit 2 is RESUME, which is explained as being used for remote wake-up signalling. Also, the relevant wake-up code is disabled in the KSDK generated for the MKL27.
Would it be possible to get confirmation that MKL27 definitely does not support remote wake up? If so, are there any recommendations for the best work-around?
A key difference between the MKL27 and other parts is that it is crystal-less USB device only, whereas the others are non-crystal-less USB OTG. I wonder if remote wakeup had to be dropped from MKL27 for some reason related to this difference.