Well I’m not necessarily saying that exact technology should be what UE4 implements.
Although to be fair we don’t truly know how optimized WaveWorks is, just because it was running on a Titan a year ago it doesn’t mean it can’t be simplified and tuned down (by loosing some unnecessary accuracy perhaps? you don’t need to simulate thousands of contact points at the hull of the ship to make it behave realistically for example…).
What I’m trying to say is that we need some kind of ocean system! The simulation of the ocean is definitely something that can be done extremely cheaply (just take a look AC III and IV) so it’s not like we don’t have enough horsepower or anything.
The main reason I ever considered CryEngine is because it has an ocean system (although nothing as advanced).
At least we had a fluid surface actor in UDK… what happened to that? 
not that it could be used to simulate buoyancy or anything but at least you could interact with water.