One thing I enjoy in iRacing that I currently can't recreate in RaceChrono is a "Compare to opt" setting.
Today the default "Compare to" setting is the best lap of the session; then I can manually choose any other lap from the same session, or add "Reference lap" from any other session.
At my current level of experience, all of my fastest laps have minor mistakes here and there. This causes the real-time time delta display to be less useful when I drive at the same part of the track again. As I work on improving my driving, I want to have instant feedback when/where I lose time against the fastest my car can go (or rather the fastest I went so far), not "what are my gains compared to the mistakes I've made during on my PB lap'.
Hope this feature request makes sense and isn't too hard to implement? I'm sure there are many others who will benefit from that too.