While I would love to see a truly successful crypto poker site, I'm not sure there are enough people around the world who could make it as popular as something like PokerStars or GGPoker. Those sites are successful, having thousands of players even at the low points of the day, but the fact they are fiat based just gives them a much higher audience.
I wouldn't say that GG is only based on fiat. They have many methods for deposit and withdrawal, including cryptocurrencies like BTC, ETH, USDT, and USDC. So even if Stake can launch a poker room and it becomes successful, it will still be very problematic for them to compete with a giant like GG. I mean, Stake is unlikely to be able to offer anything special in terms of poker that is not available on GG at the moment.