I like the proposal, though I with disagree the argument in this article setting up the proposal.

You don't need to justify a lower tax rate for all with nonsense about how good it is to help the wealthy buy more assets, as if unproductive speculation (buying something for no purpose but to see its price increase) did something good for people other than the (successful) speculator. For instance, buying stocks in the secondary market only "increases capital" to the extent that is helps to raise the price of those stocks, increasing the 'value' of the capital stock accordingly.