When compiling Kile from the sources, a live preview feature is availible. This feaueture is very usefuss. Nevertheless is is not used in official releases because it is still experimental. Ich would be nice to have a use flag, that toogles this experimental feature. Reproducible: Always
As I understand it, the live preview is something available from upstream's development Git repository, and isn't something that could be added by us. It will probably be available in the next kile release, or you can use layman to add the kde overlay and emerge the live version of kile (kile-9999).