...
The biggest reason why Monero cannot and will not be the #1 crypto is because it is developed to be 100% anonymous and untraceable. Lawmakers and regulators will not allow something like that to have widespread mainstream use.
Lawmakers and regulators will just legislate and regulate the on and off ramps and the service providers as they are currently doing with Bitcoin, and have done with cash for years.
Agree, another way is that they could opt to use the viewkey so the transaction is visible. In the same way as the current dev donation adress. If I am wrong about this, please correct me.
I looked this up and would like to add some content:
https://bitcointalk.org/index.php?topic=721045.msg9781917#msg9781917Q: How can Monero be both anonymous and transparent at the same time?
A: Monero is "private, optionally transparent". By default, you can get very little information from Monero (you can know that a transaction occured, but not whence, how much and whither).
But you can decide to give one particular person access to your balance by providing this person a viewkey, a specific string. For the moment, support is limited to MyMonero.com-created addresses, since this wallet is the only one able to take advantage of viewkeys and MyMonero doesn't yet allow reading a non-MyMonero.com-created address (such as an address created with simplewallet). But later, support will be extended to any wallet and addresses.
Another optional transparency feature, hinted at in the original whitepaper but not implemented yet, is auditable addresses.
Finally, we have also considered other methods of allowing for transparency on specific transactions. People want to be able to selectively prove payments on demand and generally open up to transparency in a controlled manner, without everything being linkable and traceable to the rest of their transactions.