Current Diff in mode is not very useful. It does not show what got changed.
It also does not fit well in new UI (screenshot form 2.360)

It would be nice to have proper text highlighting and syntax support, so users can understand what's going on.
Most of Jenkins plugins are using a Code Mirror to display different code stuff.
Lucky it's supporting side by side comparison, and it would be a great improvement to switch to it.
Example side by side view:
https://codemirror.net/5/demo/merge.html

Example implementation:
https://github.com/jenkinsci/machine-learning-plugin/pull/35/files
https://github.com/jenkinsci/workflow-cps-plugin/tree/f522e783e917bc0aa0513a29684285b710163905/src/main/resources/org/jenkinsci/plugins/workflow/cps/replay/ReplayAction

This is also interesting plugin which can be integrated with https://github.com/jenkinsci/pipeline-config-history-plugin