Ritual is a great design space.
Many concepts that make bad spells, actually make great rituals.
I want to see 5e develop the ritual design space, separately from spell design space.
For example, any character can attempt to perform a ritual. A ritual can use an Ability Check to perform successfully.
The school of a ritual might correlate with a skill.
School of Ritual (Skill)
• Abjuration (Medicine)
• Conjuration (Arcana)
• Divination (Religion: Celestial or Fey)
• Evocation (Nature)
• Enchantment (Insight)
• Illusion (Deception)
• Necromancy (Religion: Fiend or Shadow)
• Transmutation (Survival: Earth, Plant, or Animal)
The more difficult a ritual, the higher the DC. There might also be a hard character level prerequisite, so certain high-level rituals are unperformable until a character reaches a certain level.
A successful Ability Check means one performed a ritual correctly.
Interestingly, a critical failure during a ritual can mean something goes wrong. This trope of forbidden magic harming inexperienced dabblers is something D&D 5e doesnt explore. But a ritual design place is a great place for these tropes.
A ritual can be anything, for anything, with any kind of requirement to perform successfully. A ritual can be for something routine, like lighting magical streetlamps in a city, or can be obscure like that one time one really needs a Hallucenary Terrain (LOL!).
While some spell effects also have a ritual with a similar effect, spells are not rituals. There can be many rituals that are not spells.
If a spell mentions a corresponding ritual, it can also mention the DC necessary to perform the ritual successfully. Any character can try to perform the ritual, whether a Wizard or a Fighter.
Rituals are a great magic item that DMs can hand out as treasure. The obscure ones can be flavorful. Some rituals might even be useful.
Many things that are currently spells are things a caster will never prepare. But if rituals are separate from spells, then there are many spells that are terrible spells but fantastic rituals.