I disagree. The initial investments in these big currencies were from people thinking that they could become a practical currency with real-world use due to its

I disagree. The initial investments in these big currencies were from people thinking that they could become a practical currency with real-world use due to its lack of regulation and name-attached government tracking. The bulk of fiat driving up the price since then has been somewhat blind speculation. None of these change with PoS; instead, holders are now rewarded for verifying transactions.