What is "winrate" if not "winnings from individual hands" ???
Then you expressed it "/100 hands" but you could do it "/10 hands" , "/hands" or "/125485 hands" that's just some kind of representation...but to make things easier to our brain it is easier thus to have StdDev on the same scale.
It makes no sense NOT to have it in the same "time frame" as the winrate. Besides the fact that ppl probably are used to the variance numbers in /100 hands, you obviously also use it in analysis of bankroll requirements and crude confidence intervals, thus it's much easier to have them in the same time frame. I really don't see the point of changing it to std / 1 hand.