I'm prepping my next campaign for the summer and indeed am changing up spellcasters. Rather than cleric/wizard/bard/druid, I'm instead basing each "class" upon one of the deities I'm using for my campaign (a modified Dawn War pantheon) and then giving each deity class its own individual selected spell list tailored to the portfolio and spheres the deity is in charge of. These spells are coming from all the spell lists combined. As an example, here are the spell lists for Bahamut and Corellon:
BAHAMUT (Protection, Courage, Honor) - divine (CHA) caster, Lawful Good
CANTRIPS
Thaumaturgy
Blade Ward
Booming Blade
Resistance
Sword Burst
1ST LEVEL
Alarm
Compelled Duel
Cure Wounds
Mage Armor
Protection From Evil
Sanctuary
Shield of Faith
Wrathful Smite
2ND LEVEL
Aid
Branding Smite
Dragon's Breath
Find Steed
Magic Weapon
Prayer of Healing
Spiritual Weapon
Warding Bond
3RD LEVEL
Beacon of Hope
Mass Healing Word
Crusader's Mantle
Daylight
Protection From Energy
Spirit Guardians
Thunder Step
Life Transference
CORELLON (Magic, Art, Beauty) - arcane (INT) caster, Chaotic Good
CANTRIPS
Prestidigitation
Eldritch Blast
Mage Hand
Message
True Strike
1ST LEVEL
Charm Person
Command
Detect Evil
Find Familiar
Mage Armor
Magic Missile
Shield
Silent Image
2ND LEVEL
Crown of Madness
Darkvision
Hold Person
Levitate
Magic Weapon
Misty Step
Shatter
Silence
3RD LEVEL
Blink
Fireball
Fly
Haste
Tiny Servant
Tiny Hut
Slow
Clairvoyance
As you might tell, Bahamut leans heavily and takes quite a few spells from the paladin spell list, whereas Corellon takes most from the wizard list (as you might expect for the god of magic). Melora leans heavily in the druid list direction, Sehanine towards the ranger, Garl from the bard, Pelor is very fire and radiant heavy, the Raven Queen necrotic. But I went across the board in selecting spells so that I tried to not only find the ones that were most applicable to the protfolios I was using for each one... I also made sure not to give the same spell to too many deities so that there would be a true diversity for each god and thus the players would have more of a decision on which deity they would be a caster for.