What problem does this feature solve?

Example:

<template> <SomeComponent v-slot="{ SpecializedComponent }"> <SpecializedComponent /> </SomeComponent> </template>

At the moment, vue does not consider components passed as slot property on render. Instead it complains about "SpecializedComponent" being unknown.

Why is this useful:

1. Allow to render parent-child relationships in an easy way:

This basically allows to wrap the inner content of a parent component with some custom styling or whatnot.
A similar concept is used in vue-router to display the current page (<router-view>)

<template> <Table> <template #td="{ Child }"> <td style="background: red"> <Child /> </td </template> </Table> </template>

2. Allow typed components that rely on props passed to the parent component

<template> <Table :data="typedData" v-slot="{ Column }"> <Column prop="willErrorWithWrongKey" /> <Column v-slot="{ row }"> {{ row.typedProperties }} </Column> </Table> </template>

Both cases are extremely useful for different reasons

What does the proposed API look like?

See above or look at this playground