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A description of my proposed approach to Mixed Initiative Planning (mutually constraining the space of behaviour) and its relationship to the <I-N-OVA> constraint model of activity is available here.
Yes, so long as an appropriate hierarchical structure is employed. I suggest that we follow the Process Interchange Format (PIF) model of a small core representation of Process and Activity (largely compatible with IDEF) with its "Partial Shared View" (PSV) extension mechanism.
Adopt a model of plans being constraints on the legitimate behaviours in the domain. Mixed initiative is possible if all agents (system and human) involved in the planning process share a view of the planning process of mutually constraining the behaviours desired (by setting, analysing, modifying and using the constraints). This means having a model of activities that are possible in the domain, and an extendible representation for all the constraints that are possible on those activities.
Constraints naturally allow spaces of alternative elaborations of the partially specified plans.
A core process/actrivity model extendible with partially shared views (shared between those systems needing the additional information, but sharing the core or deeper models as necessary). Separation of the model from model views is essential anyway, and can support technical plan views or world oriented simulation or animation views.
We should be seeking an uniform interlingua between system components and between the various roles of users involved which seeks to communicate constraints on the mission taskings, options being explored, authority, world state, geographical/spatial, resource and other constraints. Ways to present this interlingua information in an acceptable form to the various agents (humans and systems) involved should be explored.