Chris Bartram G4DGU
I don't believe gap WGs will have much application in amateur microwaves unless low-cost micromachining becomes available.
What is attractive and not currently used in any amateur designs AFAIK is 'Substrate Integrated Waveguide'. I played with this for my own nefarious purposes just before I left GW, and it isn't difficult to make work.
Essentially, it's relatively easy to design TM-mode dielectric loaded waveguide structures which can fit within double sided PCBs. These can be transmission-lines, filters, couplers, and resonators and basically anything which you can do with conventional microstrip or waveguide. The losses are dependent on the conducting materials and the substrate. Calculation of the size of structures, unlike microstrip, isn't complicated by the consequence of the differing simultaneous propagation characteristics air and the substrate which you get with microstrip.
There is even a variant of the SIW technique called 'empty SIW' where the substrate within the structures is removed completely, and the dielectric losses are completely eliminated. That even makes it possible to make low-loss structures using FR4 as a substrate ...
Once my current unpaid employment as a house builder is completed, and I've got myself back on the air, I'll try to sit down and write something for 'Scatterpoint'.