Generally, the complaint about MtM tax is "but people have weird stuff whose value we don't know until they sell it." This is largely untrue; 3/4 of known U.S. assets are traded on an exchange. But! It's still important to get that last quarter right. And it turns out it's easy to do that. 4/

Our academic work gets into this in a lot of detail. The key point is that you can run a mark-to-market system just by waiting (for tough to value assets) until sale, but imposing an interest charge that captures the taxpayer's time value of money. scholarship.law.duke.edu/dlj/vol72/is... /5