I suggest prioritizing a JavaScript wallet as a Chrome and Firefox extension (Metamask style).
Able to do TX with a specific OP_RETURN and UTXO. To be implemented in systems like memo.cash, read.cash or BMP. Without exposing the private key.
And with the typical functions that Metamask already has like integration with hardware wallets and interaction with smart contracts (for SmartBCH and if NEXA has EVM).
This is what I need to make advanced web applications with the best usability out there. Interconnect web systems and blockchains. It is so good this strategy is called web3 and it is clearly the future.
You can build a mobile application if necessary by reusing the core JS of this extension.
This development is critical and decisive. I recommend trying to develop it jointly for NEXA and BCH. This requires joint funding and next level coordination.