Isnt a further problem than even with a LARS not all targets will be seen on primary. As I understand it gliders do not paint well, as is also the case for some composite ultra lights as originally suggested in this thread.
I appreciate they should not be in IMC but you may be descending through an undercast and there is always the risk the first thing you will meet is a glider very close to the base which is not transponding and not being painted on radar.
Of course there has never been a mid air between two aircraft outside CAS in IMC in the UK so the record is in favour of not meeting another aircraft.
I can think of a number of commercial operators that are public transport that operate outside of CAS and do not carry any form of TCAS. For example there are regular commercial flights from Shoreham to the continent who at best might get a service from Farnborough for a few minutes but are outside their cover over the channel and not within Lilles cover.