Bela,
I downloaded the latest image and burned......still won't boot on a rpi3. I can't believe I missed this, I had looked at it 10 times last night. This is the config.txt
# For more options and information see
# http://www.raspberrypi.org/documentation/configuration/config-txt.md
# Some settings may impact device functionality. See link above for details
[PI0]
initramfs 7.1beta3.gz followkernel
kernel kernel4120.img
[PI1]
initramfs 7.1beta3.gz followkernel
kernel kernel4120.img
[PI2]
initramfs 7.1beta3v7.gz followkernel
kernel kernel4120v7.img
[PI3]
initramfs 7.1beta2v7.gz followkernel
kernel kernel4120v7.img
The initramfs for the PI3 is wrong. Fixed and it boots on a pi3.....now checking the rest.
Edit: Buitin wifi connects..... iperf3 shows about 25Mbit transfer rate, which seems about par for the coarse for this broadcomm chipset/driver.