I had a similar question and from what I recall the gist is that everything in ICU is time based because cyclists do not seem to get much use out of distance (which makes kind of sense as in that sport, coasting, wind, elevation habe much higher impact than in running, relatively speaking). The dev team are cyclists and presumably the majority of users as well (I don’t know). Hence why it is as it is and why the priority is possible not very high.
Somewhat related but not the same: Activity: workout line is off for distance-based steps
All of that said, for runners a conversion between all metrics based on simple regressions over historic workouts is mathematically possible and pretty accurate in my experience, and the argument that ICU cannot know the elevation is moot - nobody expects that, and a runner usually knows whether the much shorter routes they are running matches their usual profile or not.
Best of luck, I’ve upvoted. 
BTW, I’ve gone the opposite route, I’m planning all my runs with distance instead of time. Distance is generally my primary planning metric and I find that much better suited for my needs. Irrespective of ICU.