I believe that the practice of mixing airliners with small GAT or gliders (which, as I said, are nearly invisible) is more risky than necessary
Could I suggest that the mixing of operations may not necessarily be the problem? I learnt to fly in an environment where many different types of aircraft were mixed with many other types. Uncontrolled airspace almost did not exist - but the freedom of VFR flying was still preserved away from terminal areas.
If the glider and airline are both in receipt of a suitable ATC service, could adaquate separation be performed? The fact that the glider is nearly always invisible on radar may be a problem if the glider issues inaccurate position reports? Or is the fitting of a mode-C/S transponder feasible?