To clarify here, Chainx (PCX) is already on mainnet 2.0 (launch December 2020).

This testnet you are refering is for X-BTC that is part of ChainX ecosystem. It will be new version with more features of crosschain for BTC on ChainX.
-> https://chainx-org.medium.com/chainx-x-btc-2-0-testnet-coming-soon-875a15f8c694

It all will be fully working on Polka (DOT) as one of the biggest (maybe even biggest) rely chain. (And it will be crosschain not only for BTC but also ETH and FIS are planned to be added next, and more coins in the future)

-> https://chainx-org.medium.com/what-is-the-difference-between-the-chainx-bridge-and-the-polkadot-bridge-11ab77ba359
-> https://dotmarketcap.com/coin/chainx

ChainX also will be used in upcoming decentralized encrypted message app (called Comming). Will be introduced as the database of Coming’s Identity Key to store decentralized identities on the blockchain.
-> https://chainx-org.medium.com/the-encrypted-messaging-app-is-coming-36ef197a254d

Also pretty soon (probably april/may) will be airdrop for PCX holders, for upcaming project Sherpax: