I think this might be usefull to allow (static) typechecking route responses.

For now responses content type is typing.Any, instead we could use generics.
The following doesn't yield any error:

from typing import TypedDict

from starlette.requests import Request
from starlette.responses import JSONResponse

class Coordinates(TypedDict):
    latitude: float
    longitude: float

async def valid_route(request: Request) -> JSONResponse[Coordinates]: 
    return JSONResponse({'latitude': 1, 'longitude': 2})

While this would raise a type error ("dict[str, int | str]" is incompatible with "Coordinates"):

async def invalid_route(request: Request) -> JSONResponse[Coordinates]: 
    return JSONResponse({'latitude': 1, 'longitude': 'douze'})

I know many people are using FastAPI with pydantic, but I needed to have this so I though maybe I'm not alone.

Maybe the same could be done for responses .json()?