Rolling KD-Tree?

I've seen several ways of making DC models favor recent data points:

1. As you say, add time as a feature to the data points. BeepBoop and DrussGT do this. I'm not sure if it is an advantage or disadvantage having time "compete" with other dimensions instead of it being a separate criteria for selecting points.
2. Give your KD-Tree a maximum size where older data points are deleted as new ones are added. For example Diamond's anti-surfer gun combines several KD trees with different max sizes to find the closest matches in the last 125, 400, 1500, and 4000 waves. This of course also makes your tree(s) faster!
3. Have the values in your tree store the time as well as the guessfactor. Then sort your top k matches by their age and weight them according to their rank. Diamond does this for its surfing, but not its guns. I suppose instead of ranking them, you could also weight them by 0.99^age or something, but I haven't seen that done before.

They each have different advantages/disadvantages and I'm sure there are other things you could try as well!

Adding point removal isn't hard, the hard thing is to keep the right tree structure, which I haven't seen in most implementation, which is necessary to keep the tree performant.

Removing a point is essentially:

1. search it as normal.
2. iterate through each of the bucket and erases it.