Arelith

Wizards gain a Focus status indicator, which is replenished with each tick; more rapidly with higher Wisdom.

A Wizard may choose to read his or her Spellbook in order to recover one entire spell level, (or maybe a bracket of spell levels) at the cost of an amount of Focus.

• If Focus is too low, reading becomes too difficult and the spells cannot be replenished.
• Spellbooks cannot be read in combat.
• Reading takes several rounds, making it impractical for quick recovery.
• Resting recovers an amount of Focus per rest tick, but may leave the state below 100% if it has been severely drained.

Hopefully, this will negate the need for a sub-class, because any Wizard desiring especially rapid recovery would need to build for high Wisdom.