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

Maybe you should use dynamic components rendering?

 <Table v-slot="{ Column }">
    <component :is="Column"></component>
  </Table>

@Alfred-Skyblue yes, this would work, but it gets kinda cumbersome and is very unintuitive. Usually you can just use any variable from your script section and render it as a component. Why the limitation for slotprops? The developer usually doenst know the internals and assumes that it just works "the same"

// EDIT: I just tested it, and it doesnt show it. In fact, its not visible anywhere (no console warnings, nothing in the html). Weird

it does show when i tested it in your playground

You are right. This has to be a user error on my site then ^^