The park is planning to start shooting their new Verbolten commerials "next week." My guess is that they're shooting for a Memorial Day Weekend opening for Verbolten, as they did for Mach Tower last year.
BGW has had soft openings for attractions in the past (I recall riding Alpengeist in April of 1997- about a month before its "official" opening.) If in fact Verbolten is cycling for a commercial shoot next week, it wouldn't shock me to see a soft opening.
The hang-up here would be the many unique thematic elements (mostly contained within the show building), which the park would likely want to complete prior to opening the attraction to the General Public.