MobileFrontend provides an InlineDifferenceEngine which rather than displaying the diff in a 2 column layout displays it in a single column. This seems like it would be useful for core.
renders a single column diff and replicates the functionality of https://en.m.wikipedia.org/wiki/Special:MobileDiff/687926997
The code for includes/diff/DifferenceEngine.php is pretty messy and is likely to need heavy refactoring to achive this.
This inconsistency causes confusion due to the completely different implementations: (see T123413)