Diversification always needs to be across different Asset Classes. Only buying stocks from different industry sectors is usually considered “good diversification” these days — but actually is not diversification at all. (All are in the same asset class, naemly stocks, a paper investment.)
Finally, some people appear to awake to more prudent measures. In light of Bitcon and other Crypto coins, which may well be an emerging new asset class of their own, there is an easy rule of thumb, “Bitcoin for Transactions, Phyzz for Storing Value/Asset Protection”!
Actually, I would even go A BIT (pun intended), as in a few percent, more in favour of Crypto — even for “storing value” although that’s not really what Crypto coins are particularly good at (relying on external factors for STAYING valuable, that is — even if we expect, or hope, for electricity and computing to ALWAYS be ubiquitously available)…
The “mix”, from an Asset Management (or Protection) point of view is, therefore, a matter of personal choice. We nned to update Swiss bankers’ 33-33-33 diversification advice of the 1980s to also include today’s “new asset class” though.