Lots of peeps do it. It's not that hard to do. One could simply bounce it from one country to another, set up a business, and a bunch of other things. You don't need to be a billionaire to do it.
If you decide to put your fiat money in the system, it's already clean by then, and if you put it to work earning dividends, then you are paying taxes on that income, the government will likely not go after you. They have bigger fish to fry.
The guys revealed in the Panama Papers thought it wasn't that hard either. I'd just declare it and pay tax, especially if you reside in a country where the burden of proof is on you to discharge the tax authority's accusations
*cough, Blighty
*.
Those guys in the Panama Papers did it wrong. Most or all of them outsourced the job, they should have done it themselves. Anyway, maybe there's a big difference between $10m and $100m (aside from the obvious $90m) in the way it's handled.
If I had ten thousand bitcoins and then joined a few ICOs (and got another ten thousand ETH and assorted alts) and cashed them all out at the top (an almost impossible feat), I'd have difficulty cashing out the limits daily from all the exchanges I know today, so that would be a problem. A nice one. But still a problem.