Once TaskGroups (https://airflow.readthedocs.io/en/latest/concepts.html#taskgroup) that would be released in Airflow 2.0 reach feature parity with SubDags and we have wide adoption and feedback from users about Taskgroups we should deprecate Subdags and remove them eventually in Airflow 3.0.

Discussion Thread: https://lists.apache.org/thread.html/ra52746f9c8274469d343b5f0251199de776e75ab75ded6830886fb6a%40%3Cdev.airflow.apache.org%3E
airflow/operators/subdag.py
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"""The module which provides a way to nest your DAGs and so your levels of complexity."""
from enum import Enum
from typing import Dict, Optional
from sqlalchemy.orm.session import Session
from airflow.api.common.experimental.get_task_instance import get_task_instance
from airflow.exceptions import AirflowException, TaskInstanceNotFound
from airflow.models import DagRun
from airflow.models.dag import DAG, DagContext
from airflow.models.pool import Pool
from airflow.models.taskinstance import TaskInstance
from airflow.sensors.base import BaseSensorOperator
from airflow.utils.session import create_session, provide_session
from airflow.utils.state import State
from airflow.utils.types import DagRunType
class SkippedStatePropagationOptions(Enum):