So are we assuming that Voyager somehow communicated slipstream tech information back to Starfleet via operational portions of the Hirogen network, whereupon the Vesta and Meerian-class ships were initiated? I find it difficult to accept that a 100,000-year-old comm network spanning tens of thousands of light-years just flarging crashed completely and irrevocably because of one node incident.
Or do we assume that Starfleet had a slipstream drive project already in progress, which led to Vestas and Meerians? Clearly, Meerians were already in-service by the time of the "Pathfinder" episode, which AFAIK was the only time since "Message In A Bottle" in the Voyager TV series that Voyager communicated with Starfleet.
Additionally, is slipstream drive an actual "drive"? Or is it a form of deflector-related technology? Or both? The focusing thing on the Vesta makes me wonder, as do the modified Voyager nacelles that have been written about but not seen yet.