Hello seL4 devel! Recently I was on the developer hangout meeting and brought up a ppc port. Interest seemed low, and some even called ppc a “niche” architecture which seems unfair.
There was also the much more concrete concerns of funding and overall maintenance. I believe an PPC port would be very valuable, and I plan to do a whole essay/write up of some sort, but I am also not the most familiar with the technical challenges, and could use more information on those.
I do think there is definitely people who would want to run seL4 on PowerPC platforms. PowerPC is one of the few ISAs that has existing, modern hardware without closed-source binary blobs, which I believe pose a real threat to the trustworthiness of the hardware seL4 is currently capable of running on.