Well, Steven Davis which originally designed the excalibur ship i've made for bc created the excalibur about 10 years ago, much before the Luna ever come to exist, but to be honest i don't think they share much.
Anyway, that is a matter of opinion.
As for the excalibur you'll see in ST: E, yes, it's a different ship from the bc version, yet, a natural evolution of the model; remember that the BC version was the prototype of the class, NX-90000.
All spoiler i can give you so far is that this model won't be a prototype anymore, therefore bearing the NCC registry.
And, the reason it was not entirely show so far is because we are giving it a very special treatment, to become one ship that people will surely remember.