Took a minute to snarf your 9pi2.qemu off of contrib and run it on my 8.0.0... (it wasn't there last night; depends on when 9pio syncs the web interface, I suppose)
It runs just peachy. Based on the diffs you supplied, it looks like my bcm sources (from the latest r4 ISO) are not the same as yours. I don't use 9front. What is the best way to make sure my bcm (and 9) kernel trees are the same as your current tree? I suspect we have a slight deviation that is enough to cause this kernel not to boot. Otherwise, I've added your changes to my tree...
Thanks for your time! This is helpful.
D