If you bought a Bitcoin at $500 and then it hit a capitalization of $1 trillion - you only made $50,000.. definitely nowhere near enough to retire on... Diversifying that $500 into a dozen promising alternates is likely to reap better results.
Issue of course is nobody wants to do their homework. Crypto currencies is being treated like lottery tickets by a lot of people.
I doubt that people here are in agreement that 1 BTC would be a sufficient investment for retirement - maybe 10-20 BTC - especially if BTC reaches $1 trillion market cap, as you seem to concede to be possible. It is also very possible that BTC will reach a greater than $1trillion market cap.... and it is also possible that if people diversify their investments, they still may be able to accumulate more than 20BTC over the years and to profit very well off of the BTC portion of their portfolio.
Lot's of speculation and lots of potential outcomes. There are a lot of ways to diversify a person's portfolio, and based on a lot of research, advice and assessment of one's risk tolerance and investment timeline.
As you seem to have suggested gold as a possible alternative to BTC (or a possible way to hedge one's portfolio), I do NONETHELESS think that BTC has a much greater potential for an upside, as compared with gold. I currently do NOT hold any gold NOR do I plan to invest in Gold b/c currently I am of the belief that BTC accomplishes a lot of the same dollar hedging purposes as gold but BTC is a better investment b/c of its greater potential upside.