If you just have 1 commit selected, then the Changes view always shows the older part left and the newer part right. If 2 commits have been selected, the Changes view's title shows the IDs in the correct order.

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.