This enhancement will make a difference if you are working within directories in ArcCatalog's TOC and you keep scrolling up and down whenever you are working within their contents.
My idea originated from the similar functionality in MS Word where you can split the view to browse two different parts within a big document. I use this semi daily in my work, so I thought ArcCatalog TOC should have this functionality as I struggle most of the time to go back and forth, scroll the slider between my TOC folders interacting with their contents. see snapshots below..
*Snapshot 1: View splitter in MS Word.