Here is a list of suggestions for you:
1) Turbot Fish are X-Chains of length 4. I agree that Turbot Fish are hard and that longer X-chains are Unfair. I see XY-chains of length 4 as hard and longer XY-Chains as Unfair. [this may be a taste matter]
2) X-Chains are in both directions. Usually only one direction is currently displayed. For Turbot Fish both directions can currently be displayed. XY-Chains could be also in both directions as could Remote Pairs. [Maybe consistency is best here. Either always show both directions or never show both directions]
3) For the Solving Techniques notes, one could note that Uniqueness Test 4 is the same as 2 Hidden Rectangles [if I am correct]
4) The basic SDC is hard while the extended SDC is unfair. [I believe you noted that this would be a programming nightmare]
5) Add 3D Medusa, Aligned Pair Exclusion, WXYZ Wings [maybe there is overlap with ALS?]
Diff: