I like the 2/3rd caster approach, and honestly I would turn most casters into 2/3rd casters except wizards and cleric.
buff up EK and AT to 1/2 casters(1/3rd casting really sucks)
the you would have:
full casters: wizard, cleric
2/3rd casters: Artificer, Bard, Druid, Sorcerer, Warlock
1/2 casters: Paladin, Ranger, EK, AT, +any future subclass that gives spells to basic spell less class.
as for cantrips, after 5 of them, you could have them all known. later on it's just a magic flavor.
also, what is with all extra spell slots? Is it to replace lost Spell points for missing 8th and 9th level spell slots?
if that, just bite the bullet and have it use SP by default with limit of only one 6th and 7th spell slot per Long rest.
