Daretti, Scrap Savant comes to mind for 3 of those you listed. He is very good at coming out early (turn-2ish) if you can afford top-end fast mana (mox diamond/mox opal/mana vault/etc), and he can make use of what cards you've put in the 'yard.
There's also Malfegor who empties your hand every time you cast him (for value!). Likewise, there is also Neheb, the Worthy as another discard focused general.
Unfortunately I don't think you'll be able to play Oath of Scholars because as far as I know most of the "discard for value" type cards are BR so that's where you'll most likely end up if you're trying to empty your hand quickly.
Bottled Cloister lets you have an empty hand during most of the turn cycle. There's a risk in that your hand is exiled forever if an opponent removes the Cloister, but the payoff can potentially be huge. I personally use it in my Karn deck to shut off my opponents' combat with Ensnaring Bridge, and to make Null Brooch no more costly than Negate.
For those who're interested, here is the precon deck list of "Widowmaker" that had both Null Brooch and Oath of Scholar, emphasizes on Sky/Fish strategy with some reanimation:
Which commanders would work best with these? I', thinking of Chromium, the Mutable, Dralnu, Lich Lord, and Jace, Vryn's Prodigy.
Shu Yun, the Silent Tempest WUR Voltron Control
Temmet, Vizier of Naktamun WU Unblockable Mirror Trickery
Ra's al Ghul (Sidar Kondo) and Face-Down Ninjas
Brudiclad, Token Engineer
Vaevictis (VV2) the Dire Lantern
Rona, Disciple of Gix
Tiana the Auror
Hallar
Ulrich the Politician
Zur the Rebel
Scorpion, Locust, Scarab, Egyptian Gods
O-Kagachi, Mathas, Mairsil
"Non-Tribal" Tribal Generals, Eggs
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Primary EDH; Rakka Mar Token Perfection, Crosis Mnemonic Betrayal, Cromat Villainous, Judith Gravestorm, Rakdos Empty Storm, Exava Artifacts, Bant Trash, & Fumiko Voltron!
EDH kept at home; Ruzzian Isset & Rakdos LoR!
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Latulla Burns, Akroma Smash, Jeska Voltron, Rakdos Storm, Bladewing Darghans, Lyzolda Worldgorger, Xantcha Steals your Heart, Jori Storm, Wydwen Permission, Gwendlyn Paradox, Jeleva Warps, & Sigarda Brick!
Legacy Showanimator and High Tide!
Niv-Mizzet Reborn
Feather, the Redeemed
Estrid, the Masked
Teshar
Tymna/Ravos
Najeela, Blade-Blossom
Firesong & Sunspeaker
Zur the Enchanter
Lazav, the Multifarious
Ishai+Reyhan
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-Prime Speaker Vannifar
---------------------Will & Rowan Kenrith
Unfortunately I don't think you'll be able to play Oath of Scholars because as far as I know most of the "discard for value" type cards are BR so that's where you'll most likely end up if you're trying to empty your hand quickly.
Two Score, Minus Two or: A Stargate Tail
(Image by totallynotabrony)
Black is also attractive for Insidious Dreams. Red has things like Molten Vortex and Magmatic Insight to get rid of the lands that you can otherwise only drop one of per turn.
- Rabid Wombat
For Null Brooch discard and Ghirapur Orrery to play more lands, aye? Though likely hand size would remain high with her than not.
I guess Gisa and Geralf and The Scarab God would also work due to their reanimation ability. I don't suppose Oath of Scholar would be nice in Kynaios and Tiro of Meletis and Phelddagrif? (Need DirkGently's opinion on Phelddagrif.)
For those who're interested, here is the precon deck list of "Widowmaker" that had both Null Brooch and Oath of Scholar, emphasizes on Sky/Fish strategy with some reanimation:
https://magic.wizards.com/en/game-info/products/card-set-archive/exodus-theme-decklists
Base on the list, I suppose Vela the Night-Clad would also work well with low hand size.
Shu Yun, the Silent Tempest WUR Voltron Control
Temmet, Vizier of Naktamun WU Unblockable Mirror Trickery
Ra's al Ghul (Sidar Kondo) and Face-Down Ninjas
Brudiclad, Token Engineer
Vaevictis (VV2) the Dire Lantern
Rona, Disciple of Gix
Tiana the Auror
Hallar
Ulrich the Politician
Zur the Rebel
Scorpion, Locust, Scarab, Egyptian Gods
O-Kagachi, Mathas, Mairsil
"Non-Tribal" Tribal Generals, Eggs