one thing I'm not sure I understand, why does it does it use the correct ip address upfront? (e.g. did you configure dhcp) or is that the case where dhcp is not used and you get a random ip address?

using the correct ip address, foreman would match the provisioning data.

Sorry for not mentioning that, DHCP is configured to assign ip addresses only to PXE booting machines and the smart proxy is not touching it (if that's what you mean by not used), anything else on the network needs static ip address.

I don't see this as a viable option for our current setup, which includes more than 700 machines with static ip address and nfs root configured through DHCP that won't be moved to puppet/foreman yet as first of all we want to make sure that the workstations transition is done right.

Anyway, I will stick with the php script in front of iPXE, as the setup does not require another reservation which I would have to make a request for (Company's rules), for now and hopefully this will be supported in the future.

Just for the record, the PR associated to this ticket is more of a generic and improved iPXE support in Foreman while the ticket requests support sending MAC address in unattended iPXE call. This was available for years if you had foreman bootdisk plugin enabled, in Foreman 1.17+ this code moved into core so it's possible to do this without bootdisk plugin. The parameter to send is called just "mac".