I've been (poorly) maintaining the net/isboot-kmod port for a bit. It works but it is completely out-of-tree and independent from the in-tree iscsi stack. I'd love to see this diff get some traction so isboot is no longer necessary. I'm working on setting up a test bed, including at least one Chelsio T5 10GbE NIC.

A couple notes after skimming the diff-
The code for reading the iBFT may need to be more persistent. I don't know if all NIC/BIOS/PXE implementations support reading the table from ACPI, so you may want to implement the "lowmem" scan as a fallback. I've also heard of at least one case where there are _multiple_ ACPI entries, and the desired one isn't "1". I'm working on adding a sysctl to control/select this in isboot.

The patch will also need tweaking to work with the latest IfAPI changes. See e.g. src/tools/ifnet/convert-ifapi.sh.