Short version: corporations who start a war on another corporation and it is not mutual are forbidden to dock/undock in high security systems (neither stations nor structures nor mobile depots; CONCORD would disable the option based on pilot license), forcing them to either set up a base in LS/WH/NS or refit/resupply/repair/reship in space using the tools already available. Thus non-mutual agressors would be operating like a marching army, with exposed logistic chains (neutral ships can’t assist them, they need to bring their own helper ships from their base thus making them vulnerable to attack). Also means that a character who starts a war on a unwilling target is comitted to it unless he uses an alt.
This would be independent of the general wardec mechanic, it could work either with the current model or a different one. The aim is to force aggressors into a onerous commitment, thus making non-consensual wardecs dependant on actual commitment to fighting them. Conversely, the aggressed corporation would enjoy the benefits of operating in friendly territory since they could use HS services normally.
Oh, and what about mutual wars? They remain the same, both sides can use HS at will.