I agree that the current way of navigating in a long thread can be cumbersome.
However, this isn't something under my direct control as it would be part of the Jive interface. Here is the idea space for Jive if you want to make your specific suggestion: Space: Ideas for Jive | Jive Community
But never fear -- our Jive reps have heard from me frequently and emphatically about improving thread navigation. I've been clear that this is especially important to our community, where threads can get very long and have a long life as well.