Welcome to the wild west of cube design.
The plan here is to highlight legacy+ cards in a medium powered environment centered around Instants and Sorceries. The spells-matter archetype will be interpreted and pulled in a number of directions, playing into the strengths of each color.
Decks can be divided into five main categories: Control, Tempo, Aggro, Midrange, and Combo. Control comes in proactive and reactive UB variants, splashing red for the prior and white for latter. Tempo can work in any base-blue color combination, centering around low-cmc / high value creatures alongside cantrips, counter spells, burn/removal. Aggro uses combat tricks and compatible creatures for one-attack wins, and has combo potential with Zada (and related creatures). Midrange takes the form of Naya Anti-Control / Punisher or Big Mana tokens. Combo is covered in the section below, perhaps making up the largest share of decks in a pod depending on a playgroup's preference.
Archetypes
Temur Kiln-Fiend Combo
Jeskai Zada/MirrorWing/JeskaiAscendancy Tokens
Grixis Proactive Control / Foretell
Esper Reactive Control / Miracles
Sultai Self-Mill / LabMan / Worm Harvest
Naya Anti-Control
Seasons Past 5c Control
Dimir Delver Delve
Izzet Delver CounterBurn
Combos
Thousand-Year Storm / Sentinel Tower / Gutter Snipe
Mill
Self-Mill + LabMan
Molten Vortex + Swans of Brynn Argoll / Life from the Loam
Mystic Sanctuary + Meloku / Kefnet + Extra Turns
Jeskai Ascendancy + Sorcerer Class / Noyan Dar
Sprout Swarm
Wheels + Alms Collector / Spirit of the Labyrinth
Worm Harvest
Approach of the Second Sun
CMC-matters burn