Remote kernel strategies does not work in Mathematica 12. It seem that the approach used in the original paper is explicitly blocked -- MathLink`CreateFrontEndLink is now blocked.
Moreover, in Mathematica 12 it seems impossible to attach notebook to remote kernel accessible via VPN -- Kernel starts but FrontEnd then asks kernel to connect to FrontEnd's local IP (which is inaccessible to remote kernel).
I personally found no way to make front end use specific IP address.
Overall passing IP addresses over the network expecting the other side to connect seems like FTP in 21 century :(
Said this. Kernel Configuration Options is completely broken in Mathematica 12. It does not save changes and you have to edit init.m by hand.