fine w/e
because sram are using direct mount UDH to expand get enough room to fit an extra cog on the outer side of the cassette, WITHOUT AFFECTING THE DIMENSIONS OF THE REST OF THE CASSETTE. 12sp was done the same way, adding a cog to the inside of the cassette, but there is no more room to add another cog there, and even if you could, it would make chainlines even worse than they already are.
So in order to make 14sp cassette for this derailleur, you would have to fit 2 more cogs inside the same width as a 12sp cassette. In order to aciheve that you have to:
- 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
To be fair, Campagnolo managed a 13 speed cassette which works just fine without needing UDH (even works with 12-speed flattop chains). Apparently there's already a wheeltop(?) 14-speed cassette sold on complete builds, which seems to work fine as well (however, I think using a proprietary freehub body and a narrower hub design).
Since owning one, I'm a huge fan of 1-by drivetrains on race bikes. Using a 13-speed cassette, I'm really not missing anything! Gear spacing is no issue (at least with my 13 speed setup), and lowest ans highest gears are spot on. If there's a new option for that, maybe even with 14 cogs, that would be great in my opinion!