Taxing liquid capital is fairly straightforward, especially if it’s tied to income (like company founders owning shares).

Taxing non-liquid assets is complicated because it’s hard to make it fair in cases of family home inheritance and similar situations.

But taxing use of assets as collateral for loans (to create liquidity from a non-liquid asset) should be reasonably fair, it can be treated as an advance on capital gains taxes on the collateralized asset.