For tax purposes, the complexity is roughly the same as if you traded stock shares of (say) a closely-held private Belgian company for stock shares of (say) a closely-held private Luxembourgish company.
Neither is easy to value, but the rules for doing so are well-defined.
The only thing that's new about this is that the average person can more easily get themselves into a difficult tax situation than before these tokens existed. That's in turn because of the SEC accredited investor rules and other countries' equivalents, which make these tough securities rarely accessible to ordinary folks without financial & tax sophistication. The accredited investor definitions have a lot of flaws, but not the idea behind having such a barrier.
And, indeed, the SEC and foreign equivalents are starting to pay more and more attention to cryptocurrency... The rules are still the rules, as much as people don't like it.