I think the Astral schools have a lot of unexplored potential. I'll share some ideas here.
Sun: Sun is probably the most effective and ubiquitous of the schools, but aside from Daybreaker/Nightbringer is relatively bland. I'd like to see enchants that can add on aftereffects, rather than just more damage/pierce. You could enchant a hit to leave a -30% weakness, or give you a blade after you hit, or deploy a global.
Star: Star is cool, but I feel like there's more that could be given here. I would like to see offensive auras such as Impede. A wizard would have two aura zones, an "inner" one for helpful auras you cast on yourself, and an "outer" one for harmful auras. I'd also like to see more counterplay to auras rather than just "balance gets to blow them up in your face for 1000 damage, no one else can do anything about them." Other schools getting spells that are bonused against targets with helpful auras, or the ability to remove or even invert an aura (turning a helpful one into a harmful one).
Moon: Moon has the shift spells, which are good in PvP. Polymorphs are a dumpster fire and need a complete rework. My suggestion for that would be that polymorphs apply minor stat adjustments (similar to shadow forms such as Shrike, but less profound stats and no backlash), convert your school stats in damage/critical into the polymorph's school, and give you a new deck containing spells with a higher damage per pip (no sun enchantments though). I'm not sure if that would be enough for polymorphs to see play, but it would make them less completely useless.
The Polymorph system in the moon school is the WORST mechanic in the game EVER.
As a PvE player, the Moon school is completely useless. It doesn’t “help” my own school ever. I always skip any moon school quests because they are absolutely unnecessary imo.
Like how Sun schools affect blades and spells Stars are like a buff to you (like global bubbles) Moon should be something maybe like a pip change.
The idea I’m suggesting is that Moon schools could have a “Moon Pip” which would stack on top of the currently existing at least 7 pip system. A Moon Pip can equal 3 regular pips and the conversion system would also apply on the Moon pip, meaning, players can carry a maximum of 21 pips at a time. Moon Pips would be rare pips that players could obtain starting in Celestia. You could have a moon pip rating system that plays off of the Power Pip system. Players would have a 10-30% chance (I honestly don’t know what a good chance would be but they should be more common than shadow pips but the moon pip chance would be) out of their own power pip chance to obtain a moon pip which can be increased by jewels up to a maximum of 5% per jewel. A Moon pip though would function like a single pip if the mastery school isn’t used.
You could also create blades that are from the moon school that help our existing schools that stack on top of regular blades but cannot be enchanted (they should be 10% more damage than the regular blades). You could also create moon buff spells that can only be used by one moon pip like special powerful blades etc. Just new suggestions because the current moon school system is absolutely bogus.