What this means is basically a requirement for short-term investors as well as some sophisticated long-term investors to use derivatives instead of outright ownership, such as total return swaps. If the governments involved wanted to prevent this, that would be a big difficulty. I'm not sure, though, they're even seriously opposed to such use of derivatives since the tax is mostly meant to appease the populist left, not to raise revenue. The next round of difficulties might come from the use of such swaps further divorcing voting rights from economic rights in stock ownership. Who, if anyone, will vote the shares held through swap agreements, and what incentives does that party have?