DOC: Add comment about inplace/copy proposal (#51487)

Author: phofl

doc/source/getting_started/comparison/includes/copies.rst

@@ -11,3 +11,18 @@ or overwrite the original one:
    .. code-block:: python
 
       df = df.sort_values("col1")
+
+.. note::
+
+   You will see an ``inplace=True`` or ``copy=False`` keyword argument available for
+   some methods:
+
+   .. code-block:: python
+
+      df.replace(5, inplace=True)
+
+   There is an active discussion about deprecating and removing ``inplace`` and ``copy`` for
+   most methods (e.g. ``dropna``) except for a very small subset of methods
+   (including ``replace``). Both keywords won't be
+   necessary anymore in the context of Copy-on-Write. The proposal can be found
+   [here](https://github.com/pandas-dev/pandas/pull/51466).

doc/source/whatsnew/v2.0.0.rst

@@ -818,6 +818,14 @@ Other API changes
 - Added :func:`pandas.api.types.is_any_real_numeric_dtype` to check for real numeric dtypes (:issue:`51152`)
 -
 
+.. note::
+
+    A current PDEP proposes the deprecation and removal of the keywords ``inplace`` and ``copy``
+    for all but a small subset of methods from the pandas API. The current discussion takes place
+    at [here](https://github.com/pandas-dev/pandas/pull/51466). The keywords won't be necessary
+    anymore in the context of Copy-on-Write. If this proposal is accepted, both
+    keywords would be deprecated in the next release of pandas and removed in pandas 3.0.
+
 .. ---------------------------------------------------------------------------
 .. _whatsnew_200.deprecations:
 
@@ -1424,6 +1432,7 @@ Metadata
 
 Other
 ^^^^^
+
 - Bug in :meth:`Series.searchsorted` inconsistent behavior when accepting :class:`DataFrame` as parameter ``value`` (:issue:`49620`)
 - Bug in :func:`array` failing to raise on :class:`DataFrame` inputs (:issue:`51167`)
 -