Some time ago I've been working on getting mainline linux to work on our device.
I was mostly interested in running desktop GNU/Linux, not Android, not in chroot.
I used it in Uni for occasional coding, in order not to carry lap...
Do you have an LTE version of the device or not? There might be the case that wrong firmware is loaded. Most of the rom's provide 20mhz version, while jemlte uses firmware named `BCM2076_26MHZ.HCD`. You might try to replace the file /system/vendor...
WIll I break LTE functionality permanently if I install one of the wifi only roms on my LTE kindle 8.9 HD?
No, LTE modem is connected via usb on this device so it'll work again as soon as you flash a ROM that supports LTE....