It probably wouldn't hurt to have an All Time Stones category, for consistency with other games. Even Sonic 1 and the MS/GG games have categories for this, and Chaos Emeralds basically do nothing in those games too.

The main issue with adding an All Time Stones category is at this current point in time, there is no interest expressed by the community currently. Having an empty category on a leaderboard looks bad, and creating one just to fulfill one person's wish isn't a good enough reason. The only way that it could be considered is if at least two people ran the category, which would be a bare minimum. This can always change in the future however, but right now, it's simply just not a plausible idea.