Folks, what we need is a system that warns of ANY aircraft that is about to come too close. The major flaw of most approaches is requiring that the other guy be properly equipped. It is not human nature for people to agree so there will always be many avoiders, contrarians, competitors, and folks too poor to comply even if they want to. Mutually inncompatible systems will proliferate and no single collaborative system will make more than a dent in the collision threat.

We as PICs should take upon ourselves the responsibility of not flying into someone and being aware of impending traffic - I mean beyond 'See and Avoid'.
A simple device that warns of impending collision would focus our attention to taking evasive action. It would not need to be very sophisticated, but some simple indication of direction would make it more effective.

Radar may be the most practical way. Detection at short distances does not require much power, nor equipment sophistication.

Some observations -

Flarm appears to be the best thought out existing system. PowerFlarm should be called Low-power Flarm because it operates as an unlicensed low power ISM band gadget. Range and reliability are limited due to lack of signal strength. IMHO, the FCC denied licensing of Flarm and refused to allocate spectrum to protect the inferior ADS-B already chosen for Nexgen.

PowerFlarm is priced out of reach for most glider operators. Clubs usually don't have it in their ships.

I live near a Class C airport. Only about 1/4 of the traffic I detect in the area is currently squittering ADS-B. Devices like Stratux don't yet show the majority of existing traffic.

IMHO, aircraft traveling too fast to see and be seen (maybe 175 Kn) should have active radar, to avoid anything from drones on up.

The brave new world of Software Defined Radio/Cognitive Radio is a godsend for quickly developing new technology, including radar. The open source community has embraced the technology!!!

Of my many close calls, only one was a glider, half were military, and about 3/4 came from behind me. I sure hate hearing engines from within a glider!