This is a desire but more realistically i think is a bug or a missing feature!

Before in plasma vlan support worked perfectly until someone has decided to remove it. 
https://cgit.kde.org/plasma-nm.git/commit/?id=aae4b7886bcf865d976e98910e24b13436521f8f&h=Plasma%2F5.10

Me and my company think that's not the right thing. We've installed kde distributions because we work with networks and plasma has fast support in creating network profiles and vlan. Even windows has support for vlan and its is a desktop use! But vlan creation is not as fast as it was in plasma. I do not understand why to remove a very convenient function that has always worked. Please reapply it.

Thanks for attention.