puzzles based on specific times for different openings would be nice but I don't see how it can be well implemented. Lichess has this feature but a lot of the times it's just normal puzzles where the game happened to start with the chosen opening. Having puzzles dedicated to ideas in the Sicilian(like attacking whites castled king on the queen side) would be pretty cool if implemented
i'm working on the Sicilian this last week, to great effect, and well, i'd like to improve even more with puzzles8)