I'm not sure the airspace has anything to do with it; it's the mixture of traffic. The point being that 2 small a/c at slow speeds did not miss each other by looking out of the window, and the glider has a bubble canopy. We do not yet know the relative flight paths, and perhaps never will. I wonder how much effort AAIB will put into it. After watching the Air Crash Investigation between the French Turbine commuter & a Cessna orbiting near SS France it was amazing the lengths the investigation went to to determine the lack of visibility from each cockpit and bad luck involved.
However, here was a collision by 2 small slow a/c being flown by MK.1 eyeball. There are those advocating that relative high speed (250kts) airliners can mix it with & avoid slow moving stealthy gliders with Mk.1 eyeball and also expect the glider to do the same. In the time a glider takes to make a 360 the jet, which was invisible, is now full in your face. The jet has a wide cockpit with not so good 180 degree vision from one seat. Searching for and locating a slow moving small a/c, which you don't even know is there, is not the easiest task, and perhaps not the top focus of a jet crew making a descending arrival into their destination.
All that is being discussed is that IFR commercial traffic does not have to mix it with silent invisible GA VFR traffic during approaches/departures. Remember, over the nose, and slightly below, visibility in a jet climb out is zero. It's worse than descending arrivals and all so unnecessary. Don't need to change the rules, just the airspace.