Hi,
Debian backports provide newer kernels but there are no newer firmware that should go hand-in-hand, I use Debian on somewhat new hardware and had to install newer kernel from backports, but I needed newer firmware as well (firmware-iwlwifi particularly) to fix instability with Intel Bluetooth and I did this by adding testing repo, it would be nice if testing firmware is available in backports as well.
Another thing that would be nice to have in backports is newer libva2 (and related packages libva-drm2, libva-wayland2, libva-x11-2). VAAPI hardware accelerated video decoding is not working in latest Chromium based browsers like Chrome, Brave with libva2 from stable, libva2 from testing works but it pulls libc upgrade and creates FrankenDebian.
Cheers!
Vuk Mirovic