I was wondering, what if you did a speedrun with somebody and they played on a PC and you played on an Xbox One for the run (for example). You can only select one platform for your run. So there should be a feature where you can include both platforms.

Definitely a good idea.

Until this happens to be added, I guess just note it in the run description or something.

Actually this feature of allowing multiple consoles are needed for some multi-games leaderboard too