Thanks for the reply.
In BPMN 2 an Activity is the closest to a subject area. This also applies to UML and Strategic Modeling. However, I am not entirely sure that all subjects areas can be modeled as an Activity. In fact, I am not even sure if, in a real business, a Subject Area is an Activity (but this a little bit academical).
A subject area model diagram is very similar, in my mind, to a Value Chain diagram available under "Strategic Modelling". But I find that diagram somehow limited because it forces Primary Activities to be arrow like and only allows for 1 row of Primary Activities.
In my mind, the solution entails using a diagram similar to a Value Chain diagram, but more complex, without using arrow like activities, allowing more than 1 row for primary activities, allowing nesting activities, and allowing a variable number of rows per block of activities.
Happy to customize EA but I am not sure how to go about customizing a diagram like the one described in the previous paragraph.