"If you're leaving your stuff in cryptocoin form I don't think you would pay capital gains."

Note this is only true if you hold onto particular coins. If you exchange some bitcoin for etherium, for example, you will realize capital gains or losses. This has nothing specifically to do with cryptocoins, the same thing would happen to you if you bough silver, say, and then exchanged it for gold.

Your latter point is straightforward tax evasion and will be caught or not in much the same ways as other forms.