Why no mention of a simple wealth tax? The Swiss take 1% of each citizens’ wealth, including unrealised gains on capital market holdings, every year. Paired with a policy of zero cap gains taxes on individuals - unless cap gains are that individual’s sole or major source of income, in which case they are taxable as income - this appears to strike the right balance between raising revenue and encouraging investment, without frightening off too many rich people.

Seems much more straightforward than faffing about with unrealised gains.