There is a long post about this issue
long story short, the only hope is that Coinbase decides to support the IoTeX native blockchain (in such a way that you will see your native IOTX credited), or they decide to send back the tokens in whatever other way.
Unfortunately, the exchanges are in control of the deposit addresses they provide to their users: if you send the wrong type of token to an exchange deposit address, only they can send the tokens back (although this is very rare, it seems in their recent replies to users Coinbase is hinting at some possibility of recovering the tokens “if they decide one day to support the IoTeX native blockchain”.
I guess the more users complain about this problem, the higher the chance…