Liquidity is more about altcoins not about Bitcoin. With Bitcoin, a common and accurate term is Trading volume, not liquidity.
Many years ago, when Satoshi Nakamoto was asked about transaction volume of Bitcoin and his anticipation in future, there was an answer that is still valid today.
Right. Otherwise we couldn't have a finite limit of 21 million coins, because there would always need to be some minimum reward for generating. In a few decades when the reward gets too small, the transaction fee will become the main compensation for nodes. I'm sure that in 20 years there will either be very large transaction volume or no volume.
The answer is about transaction volume, not trading volume but if people use Bitcoin for more transactions, there will be higher demands to trade it so trading volume will become higher consequently.