It's not a revolutionary idea. That I know of, the Netherlands does it, somewhat. How it works is: rather than taxing capital gains, with its myriad loopholes and counterloopholes, you tax assets directly: assume a neutral sort of "risk-free" rate of return, and then tax a percentage of that. E.g. assume yearly return of 1% on cash and savings, 6% on other assets, etc, then levy tax of 30% on that (past a tax-free allowance of 25k€ per person).
Simple, and more effective!