If I were to guess, and this is just a guess, I'd say some time during or at the end of Exposition. Considering the shop and EP items can ONLY be used during Expo and there will be no shop post launch.
Edit: Also the "layaway" option for Pledge Packages will be closing soon because Domain and Land Selection are on the horizon. So if you intend to layaway a Pledge you'll want to do that soon. And keep in mind you must have your layaway paid in full by the time of Domain Selection in order to pick a county/duchy if you plan to pledge in those tiers.