Not convinced either way whether having the same interface for all of the stack is a good idea or not, but it did remind me of Joel Spolsky's blog post on leaky abstractions http://www.joelonsoftware.com/articles/LeakyAbstractions.htm...
The thing is, Eve isn't an abstraction layer over your existing layers, it's a set of choices you can make layer-by-layer to swap out the old "unique" way of doing things with Eve's more uniform way of doing things. The unique way was arbitrary anyway.
Like, if the whole world all decided to start speaking Esperanto, that wouldn't create too much of a leaky-abstraction issue.
The one issue I can see is how to scale when you use it as your database layer and make fancy queries. But every database's query engine has its own implementation challenges and I don't think Eve is special in that sense.