Eh. I assume the level just floats from then on, probably maintained as a relative thing. It could reference inflation, but that seems too crude and gameable. The ideal curse/blessing would have a threshold that floats with time, just maintained at whatever the equivalent of a billionaire is at any given point in the future. This could probably be defined as some multiple of the median household income. Then no matter what the local economy, currency, or technology is like, any time someone exceeds X times the median income or wealth of the average person in their society, they go poof.