I have been intending to try out the new raspberry pi updates too for 9front, but haven't had the chance yet.
A couple of years ago I was building the sd-card images for my raspberry pis by using qemu to bring up an x86 install of 9front and doing a cross-compile within to build the new disk image. Here's a script that I used after the manual 9front install to do that plus a bunch of other things that you probably don't care about. It does need significant cleanup and updates.
I'm hoping that it is at least some help to others.
Chris