What does the mobile/desktop application have to do with anything? That is not the integration point, the blockchain is. The mobile/desktop application is merely an interface/GUI for interacting with the blockchain. Your "wallet" is on the blockchain in the form of your calculated transactions.

Also, you can use your mnemonic/passphrase in multiple mobile/desktop applications at the same time (not a good idea, but can be done) and should they use the same derivation path, you would see the same address and transactions. The mobile/desktop application does not "store" your crypto, the respective blockchain does. Your crypto is not actually "in your pocket", it is on the blockchain, only your access, the keys to your crypto is "in your pocket".

To which, polkadot and kusama chains are already integrated. So, just add them with your receiving address like any other.

Integrating individual mobile/desktop applications is pointless and waste of resources as it would provide nothing. It is NOT the same as integrating custodial services like an exchange or Nexo, BlockFi, Celsius, etc.

Thanks Dan! Really NEED this.