> If someone takes a loan out against an unrealized gain, that should immediately trigger a tax event.

How does that work when a house is used as collateral on a loan? Or artwork?

The loans are just a symptom, the problem is in the Estate Tax, and those loans are being used as a tool to wait out the clock and then dodge dynastic taxes entirely.

Remove the final loophole, and they'll stop playing weird games to get there all on their own. Plus it'll be way less-disruptive to everyone involves in regular loans for regular reasons.