Don't add scry, just cut the cost by 1 mana:
Gigacantrip
U
Instant
Draw a card.
Replicate 1U
The difference between Cascade and Replicate is just about the difference between a sorcery and an instant anyway.
I could definitely go with that. I wonder, though, about R&D approving of 1UU/instant/draw 2 cards. I think that is perfectly fair, but they are really hating on blue right now, and I doubt they would make something that cool.