In order to use rituals, most casters will now have to have the spell prepared. Which sorta ruins the idea of rituals - and nullifies a couple of key ways that I used my evoker.
The rest of this discussion is an attempt to address the folks that say "wizards have too much versatility" as well as to allow other classes to access some of that versatility. I'm going to focus my description and discussion on wizards and int, but you may extrapolate to clerics and wis as you desire.
Proposal: Give ritual casting to all classes.
Ritualbook: All classes can have a ritual book in which they store the recipes for rituals. Wizards have a spellbook that duals as a ritualbook.
Adding spells to the ritualbook requires that the character have 10+spell level int modifier. In addition, when a player wants to add a spell to the ritual book, they must decipher it through help from someone that already knows the spell or through the use of a read magic. Once deciphered the character must learn the spell through study and copying it into the ritual book. I propose a chance to not learn the spell similar to 2nd Ed AD&D where 9int had a 35% chance to learn and 18 int had an 85% chance to learn a spell. New levels allow new rolls.
To 'cast' a ritual, the character must know the spell, have the spell in their spellbook, have the proper int score, and have their spellbook open and available (unless they have the spell prepared in which case they can cast the ritual without these things).
In this way, other classes could gain access to a wide variety of rituals like knock and speak with dead to increase their versatility. I suggest some other spells like fly might have rituals.