Why Ethereum, why not any other altcoin? Maybe even some altcoin which even has not issued yet. If something is second at the moment it doesn't mean that it will ever be first. Ethereum with its advantages had a lot of time to overcome bitcoin but it didn't do that. I guess its characteristics are not enough for that. And when some altcoin probably will overcome bitcoin IMO it will be not the first in crypto but the first in some new definition. Of course it is just a matter of time, but I don't think we'll see this in next few years.