It turns out that Brother doesn’t seem to be very serious about publishing driver packages that work for ARM machines. The easiest way I’ve found to deal with this so far– and still have quick, good-quality color printing– is to use the MFC-9840CDW PPD. Verified working on HL-3170CDW, MFC-8480DN, and I’ll test it on HL-2170DW and HL-4150CDN printers soon. I set up Samba and avahi-discover so I can have AirPrint, and although fidgety to set up, it does seem to work.