I'll answer this on a personal level, because I think any answer to this will vary. I also think "practical" is a hard word, because I'd argue that any research that brings us a better understanding is practical in of itself, but might not immediately lead to better diagnosis of treatment. With those caveats, the research I'm most excited about relates to individual differences research. People who stutter aren't homogenous in any way, we don't even all demonstrate outwardly disfluent speech! Some of our own research has touched on this, showing that adults who stutter with different traits, abilities, experiences, goals, etc. experience stuttering in fundamentally different ways than other people who stutter do. I think in 5-10 years we will know not only more about the stuttering condition as a whole, but how subgroups experience it. That, I think, will directly lead to better diagnosis, treatment, AND empathy.