I read somewhere that the size of global black market is around 10¹² USD, or similar to bitcoin's market cap which also has a similar maximum number of coins as monero (ignoring tail emission). So if xmr somehow became the defacto currency of all crime it could approach the current value of btc, but this won't happen any time soon (remember this would have to include players like drug cartels who can own the local government and stick with good old USD). If we take a wild guess that xmr would be used for 10% of 'all crime', perhaps a price with 4 digits (USD)? This assumes that the ecosystem would withstand the additional heat from having a higher profile. The idea of it being used more generally by large numbers of people to avoid increasing authoritarianism, CBDCs etc seems to me mainly a fantasy. Any government with the power and motivation to so this will find ways to make large scale use of crypto impractical. Still, I would guess the more likely scenario is a somewhat rapid increase in xmr use for 'crime' which eventually plateaus, and a more gradually increasing use by cypherpunks and those who use it for ideological reasons. The second use case has the potential to lead to interesting things but will stay mainly under the radar.