Comment 13 for bug 1664844

Just to clarify, it's not ever possible to /block/ boot with systemd. Even if all networking is required to complete a boot, but all of them fail, the system will come in "degraded" state. But as much as possible, will be configured.

What one can affect is boot ordering, and what is required to reach certain targets quicker. For example, it sounds like for the systemd-networkd-wait-online.service you may want to extend --ignore= argument with the interfaces that are "semi-managed". They are under networkd control, but one does not care about them during boot.