"Allow moderate spellbook bloat, give special high-level spells to more kits, and lean harder on the "focus access" mechanic to make kits like the Hivekeeper more special (imagine casting Insect Plague at 7th level! )"
I personally really like this option. Combine this with keeping the highest level versions of spells kit specific (like creeping doom for hivemaster), and the usual kit special abilities/equipment quirks, and kits should remain unique.