That would be helpful.
This is the only problem:
Let's say you joined 2 years ago (730 days), and you have played 2000 games, but you stopped playing after the first year.
By using that equation, (2000/730) your qi per day would be roughly 2.74 qi per day. But, your qi per day would actually be roughly 5.48 (for the first year), and 0 (for the second year).
I think the only way to tell if someone is active would be:
(days ingame/qi)
Days ingame would be found by ever day that someone earns at least 1 qi.
If this formula will be used, I think that this suggestion should definitely be added.