I'm personally interested in this upgrade so took a shot at upgrading locally.

The patch 0001-Allow-using-obexd-without-systemd-in-the-user-sessio.patch is very problematic, and the only issue on my end. It started breaking things in BlueZ 5.73. Some of the changes are now in upstream, and some have been removed which creates conflicts. I wonder if this patch is even relevant today? it's ~8 years old

After removing the patch, bluez5 builds fine on my end after upgrading via devtool.

I can submit a patch to this mailing list for review if it helps