This is available since ages. Just stage the parts of the file in the Changes view (non-compact display) or even better using the Index Editor, then commit.

Currently, the Output view uses a tree control which does not support word-wrapping.

This is not a common task for 99% of the Git users.

These 3 rows should indicate a pile of files.

This would be hard to implement because one can select files from different repositories. The light-weight variant https://smartgit.userecho.com/communities/1/topics/301- is implemented now.

Please try with a portable bundle (no previous settings).