Think outside the box. The applications for variable speed derailleurs go beyond just regular bikes. There are folding bikes, mini velos, commuters, cargo bikes, etc. that can benefit. A 3 speed cassette weighs less than 70g. A folding bike with no shift cables, 1x chainring and 3 speed cassette sounds pretty reasonable.

If 14 speed cassettes are doable why not? No one is harping about SRAM going 13 speed, so what's the difference?

• Tighten the spacing between the cogs, which would make shifting performance much more sensitive to imperfections in setup and require thinner chain plates, which would negatively impact chain durability,
• Make the cogs narrower. The reduced volume of material negatively impacts durability and gives you less room to work with to shape shifting ramps and worsening shifting performance

Congratulations on the build.
 I'm also waiting for two FM316 frames and was a little skeptical, but now that I've seen your build, it's fantastic.
 I wanted to ask you a few questions:
what brand and type of bottom bracket did you use?
As a crankset, did you use a standard DUB spindle with a single chainring with how many teeth? Do you think it's possible to build a 48 or 50 mm single chainring with a wide axle?
What size is the bike and how tall are you?
What size is the saddle height?
Sorry for all the questions, but I'd like to take this opportunity to understand a few things about the frame.

So today for you DFS is better that XCMS? If you need buy a new set your first option will be DFS?

Regards,

William

• DFS 60/65mm – 25 mm inner, U/V profile, 5 mm carbon spokes, 1231 g, 100 kg load limit
  XM CarbonSpeed 50/60mm – 24 mm inner, U profile, 5 mm carbon spokes, 1196 g, 120 kg load limit (sold Monday)
  ZEN 40/45mm – 24 mm inner, U profile, 3.1 mm carbon spokes, 1046 g, 100–110 kg load limit
  ZEN 45/45mm – 24 mm inner, U profile, Sapim CX-Ray spokes, gravel hubs, 1306 g, 100–110 kg load limit (winter training wheels)