Update from feedback

Author: rhshadrach

web/pandas/pdeps/0011-dropna-default.md

@@ -25,7 +25,8 @@ print(ser.value_counts())
 dtype: Int64
 ```
 
-users may be surprised that the Series can contain NA values. By then operating
+users may be surprised that the Series can contain NA values, as is argued in
+[#21890](https://github.com/pandas-dev/pandas/issues/21890). By then operating
 on data under the assumption NA values are not present, erroroneous results can
 arise. The same issue can occur with `groupby`, which can also be used to produce
 detailed summary statistics of data. We think it is not unreasonable that an
@@ -43,11 +44,35 @@ This is correct, except that NA values in the column `a` will be dropped from
 the computation. That pandas is taking this additional step in the computation
 is not apparent from the code, and can surprise users.
 
+###
+
+### Keeping the default `skipna=True`
+
+Many reductions methods, such as `sum`, `mean`, and `var`, have a `skipna` argument.
+In such operations, setting `skipna=False` would make the output of any operation
+NA if a single NA value is encountered.
+
+```python
+df = pd.DataFrame({'a': [1, np.nan], 'b': [2, np.nan]})
+print(df.sum(skipna=False))
+# a   NaN
+# b   NaN
+# dtype: float64
+```
+
+This makes `skipna=False` an undesirable default. In the methods with `dropna`, this phenomena does not occur. By defaulting to `dropna=False` in these
+methods, the results when NA values are encountered do not obscure the results of non-NA values.
+
+### Possible deprecation of `dropna`
+
+This PDEP takes no position on whether some methods with a `dropna` argument should have said argument deprecated.
+However, if such a deprecation is to be pursued, then we believe that the final behavior should
+be that of `dropna=False` across any of the methods listed below. With this, a necessary first step
+in the deprecation process would be to change the default value to `dropna=False`.
+
 ## Detailed Description
 
-We propose to deprecate the current default of `dropna` and change it to
-`False` across all applicable methods. The following methods have a dropna
-argument, those marked with a `*` already default to `False`.
+The following methods have a dropna argument, those marked with a `*` already default to `False`.
 
 ```python
 Series.groupby
@@ -68,10 +93,15 @@ DataFrameGroupBy.nunique
 DataFrameGroupBy.value_counts
 ```
 
+We propose to deprecate the current default of `dropna` and change it to
+`False` across all methods listed above.
+
 ## Timeline
 
 If accepted, the current `dropna` default would be deprecated as part of pandas
-2.x and this deprecation would be enforced in pandas 3.0.
+2.x and this deprecation would be enforced in pandas 3.0. In pandas 2.x, `FutureWarning` messages would
+be emitted on any calls to these methods where the value of `dropna` is unspecified and
+an NA value is present.
 
 ## PDEP History