In order to solve the Capital in the 21st Century, we need to follow Robert Solow's implicit solution in decreasing the same underlying cause of r and g. Since most of the underlying causes of r and g are common, the only way to decrease equality is a proper formed of Engineered Recession.
What makes a proper Engineered Recession?
By looking here, may be an indication to a plausible type of proper recession, but to engineer a recession similar in characteristics to the (dot)com bubble is only possible through innovative technological crash. In other words, a large technological leap will signal a plausible Engineered Recession if technological growth slows down significantly and the underlying owners of particular Exclusive Assets have these asset value crashing. Exclusive Assets need to be a group of asset that only the "rich" own, and the majority of the middle class do not own these assets in their collection of assets. Thus, we need to pop bubbles of "rich" assets.