hey there, i just bumped into shiftphone, as i maybe could get my hands on an old one for 30 EUR. so i wondered, if there is anything going on, to get in contact with them? i found this (maschine translated) on the website of shiftphone:
Alternative operating systems: In principle, we allow any software modification on your SHIFTPHONE without loss of guarantee. Unless you make changes that damage the hardware (e.g. by overclocking). The upcoming SHIFT6mq in particular is designed to be able to use operating systems other than Android. On older devices (SHIFT4, SHIFT5, except SHIFT5me) there will probably be no alternative operating systems.
We offer various developer communities extensive custom ROM support to test their operating systems on our devices and make any necessary adjustments. However, we must not advertise that other operating systems can also be installed on our SHIFTPHONES. You will get more information. but from the community of your favorite operating system.