Just used my entire day's allotment of turbine points to make a Greater Twilight shard - 28 greater arcane, 4096 lesser arcane, and 49 Siberys dragonshards.
Effect: -20% ASF, very nice
Restrictions: Only light/medium/heavy armor with ASF
Can't put it on a Docent, can't put it on a shield, despite the fact that twilight effect is found on shields in game.
Same restrictions apply to the regular Twilight shard (-10%ASF)
I could see some potential for this to be used if we could at least put it on a shield, despite the ridiculously high shard cost compared to other recipes...