This isn't a jeskai deck. It's just running 2 white catchall cards, and 1 walker and very occasionally needs a white for flames. You will only have a white card to cast t4 50% of the time. If you cycled a censor by then you are 80% to have a white source (on the play!).
I'm playing even less White than you do (my catch-all cards are blue and I don't run the third manland), yet Wilds+Plains I think are still necessary to ensure you can Flames if you need to.
The 3 power are not necessarily needed turn 3, they're needed later down the line; but I do want to have White available turn 6 if I have to sweep a board of Zombies buffed by Lord of the Accursed/Mastery. There are some games where you don't have time to play your selection spells to get there, so I don't want to rely on them; and I would want to do so even less if I also run Cast Out.
Maindeck card choices are always debatable, but I wouldn't mind defending the picks, it's a bit quiet here
Well, alright.
-Fiery Impulse. You're not killing a Copter with it early, and while the third point of damage is relevant later I'd still prefer the exile provided by Magma Spray. Furthermore, I don't wan too much early interaction as especially Impulse and Spray get a bit worse late. I'm running the fourth Magma Spray and the 26th land over them; could see cutting the fourth Spray for a tech card (Blessed Alliance maybe)
-Cast Out. As stated I like to remain in my main colour with catch-all removals and run Commit // Memory. The card has a few advantages over Cast Out (being able to get flashed back by Jace/Hulk, not being vulnerable to enchant removal, added utility for the rare cases you want to cast Memory (yes, these do turn up)). While you need a counterspell ready to stop the threat hitting the board again, you also need that to protect the Cast Out enchantment - possibly more.
-Dynavolt Tower. Since your deck's win condition generally is not to burn the opponent out, I think Tower doesn't deal enough damage to close out a game on its own, and it doesn't do enough to affect the board state late game. I think Jace, Unraveler of Secrets works a lot better as a threat - as long as he sticks you're generating card or tempo advantage. Tower generates neither.
-Hieroglyphic Illumination. Yes, draw is good, but Glimmer is better and I want an additional counterspell. My list runs the second Pull and the third Broken Concentration over them.
For reference, my list:
Creatures (3):
1 x
Jace, Vryn's Prodigy1 x
Disciple of the Ring1 x
Torrential GearhulkPlaneswalkers (3):
1 x
Nahiri, the Harbinger1 x
Jace, Unraveler of Secrets1 x
Chandra, FlamecallerSorceries (2):
2 x
Radiant FlamesSplit (2):
2 x
Commit // MemoryInstants (26):
4 x
Magma Spray3 x
Censor2 x
Essence Scatter3 x
Harnessed Lightning2 x
Scatter to the Winds3 x
Broken Concentration3 x
Glimmer of Genius2 x
Confirm Suspicions2 x
Pull from TomorrowLands (26)
1 x
Plains4 x
Island4 x
Mountain2 x
Wandering Fumarole2 x
Praerie Stream2 x
Glacial Fortress2 x
Clifftop Retreat2 x
Sulfur Falls3 x
Aether Hub4 x
Evolving WildsSideboard is untested for me, but it'd look similar to yours:
2 x
Dispel2 x
Thing in the Ice3 x
Blessed Alliance2 x
Spell Queller1 x
Kefnet, the Mindful2 x
Dynavolt Tower1 x
Chandra, Torch of Defiance2 x
GlorybringerNot sure about it; maybe Cast Out or Tutelage deserve a spot.