Could I make an alternative suggestion? All powered aircraft that are IFR certified have a transponder. A portable PCAS receiver costs about £350, will run on two AA batteries for 6 hours and would fit in any cockpit. If the gliding community equipped with this and the powered people who worry about this get FLARM, then we can all miss each other with no huge outlay on either side. Remember only 1% of PPL’s have an IR, so this is a very small minority on both sides.
Rod1