Eh, an exception for a primary home is common throughout the tax codes and the like. Just saying you realize capital gains on an asset used to secure a loan (unless it's a primary residence) would cover that without being out of step with everything else.

Sure, a billionaire could then use their $143M estate as collateral on a loan to avoid realizing the capital gains, loophole, but since you can only have one primary home, it's a very limited loophole.