Should enterprise architecture (EA) be a shared function or a discrete function?

EA is generally a poorly defined IT role so of course it would depend.  The more "ivory tower" the EA practice the more likely value will manifest from it being centralized.  The more Solution Architecture focused tends to benefit from a discrete EA function.  

The C-Suite seems to love the idea of the "single pane of glass" through which things can be rationalized.  If you are in a frothy or disruptive industry - shared services should be kept to a minimum.