The ASK13 was only economic for Schleicher to manufacture because many bits were farmed out to local handymen to make (wing ribs etc) and there were quality control problem that showed up later. Under EASA they would cost more than a ASK21, there are significantly more man-hours and little difference in materials.
A competent maintenance organisation will prevent recurrence of the previous VGS problems, and civilian registered DG Acro's aren't falling out of the sky through maintenance problems (or age related structural ones).
I can't imagine that operating a mixed fleet of Grob and ASK would be a problem, there was a mixed fleet or Cadet 3 and Sedburgh for many years, but the short solution from here has to be getting 'as-new' Vikings back in the sky for the next 10+ years.
I doubt that those responsible for the scandal and the pedestrian sorting-out process will ever be held to account, but that's another story.