As long as Bitcoin can be shown to be a hedge against gold, there will always be people who buy it.
You fail to explain the logic. If gold is a hedge to stocks/bonds, than stocks/bonds are a hedge to gold. So you already have a hedge.
Investors may be spicing-up their portfolios with cryptos, but that doesn't mean that existence of gold guarantees the existence of Bitcoin.
Plus, in your own portfolio-split example, you didn't put "Bitcoin" but "cryptocurrency". These are not synonyms. Even if gold, in some magic way, warrants the demand for cryptos, it doesn't mean that Bitcoin will survive, it can be replaced with other coin.
60% equities
30% bonds
6% gold
3% cryptocurrency
You're missing 1%.