I think that XRP is quite likely to pass BTC in cap, but I don't think Coinbase will have much if anything to do with it - rather it will be real world use of the token in the banking sector. Difficult to say how far away from this we are, but once one bank starts using it properly and gains an edge on every other bank, then the others will certainly follow - that is when the XRP price will truly explode. $1 trillion cap doesn't seem unreasonable.

On a side note I also think it's likely that a smart contract coin can overtake BTC in cap. ETH still looks the strongest contender. I like Cardano, but the price is way too high for something that is so early on in development.