How much would billionaire philanthropists need to scale up their giving to meet the Giving Pledge in their lifetime?

The idea of creating a billionaire impact list has been floating around for years. Some people might already be working on it, but I haven't heard anything recently.

Here is another feature that could be added to such a list: 

1. Take the list of billionaires who have taken the Giving Pledge.
2. List their current wealth and their previous yearly donation amount.
3. Based on past growth of their wealth and annual giving trend, calculate when they would be expected to have donated 90% or 99% of their wealth.
4. Estimate whether they are on track to donate 90% or 99% within their expected lifetime.
5. If they are not on track, calculate by how much they would need to scale up their annual giving to accomplish donating 90% or 99% of their wealth within their lifetime. 

IIRC, there was a post by @Benjamin_Todd where they estimated the annual donation amount of the Bill & Melinda Gates Foundation and the wealth of Gates. I think the bottom line was that even though the Gates Foundation is donating billions of dollars annually, the total wealth of Gates is still growing, and their annual donations would need to be scaled up massively to achieve giving 99% within Gates' lifetime. 

(Unfortunately, I can't find the post right now. It might have been a tweet. If you point me to it, I will edit this.)

Presumably, this is the case for most billionaire philanthropists. Creating visibility around this "giving too slowly" issue might motivate billionaire philanthropists to donate more money sooner. 

It appears to be difficult to donate tens of billions of dollars effectively. I had the idea for this post while listening to the Hear This Idea podcast, Rory Stewart on GiveDirectly and Massively Scaling Cash Transfers. It offers a bold vision of how unconditional cash transfers might be an intervention that could be effectively scaled up to use hundreds of billions of dollars of donations. Maybe billionaire philanthropists who are "giving too slowly" might even be nudged to donate billions to GiveDirectly.