The EIP is looking good so far and I’m happy with the specification to be implemented.
I would only suggest that we keep JSON-RPC requests consistent and only use hexadecimal encoded values on the parameters.
Just as eth_chainId returns the chainId value hex encoded, we should also pass this parameter and networkId on wallet_updateChain value hex encoded.
However as @danfinlay pointed out here, the EIP-747 uses decimal values but I since this EIP is also on Draft, I personally would like to suggest to change it also to have only hexdecimal values.