ADSB is not mandated in Europe. The CAA wanted to mandate SSR in UK but
this was sent down pending the development of low cost / low power ADSB.
This is now available from Uavionics at about £400. At that price I expect
a wide take up in the UK. Why wouldn't you want to know about spam cans,
CAT, drones, and helicopters as well as gliders and why would you want to
hide from ATC??

So in practice the rule makers for gliding competition cannot ban
conspicuity / situational awareness tools from the cockpit as this would
compromise safety. The genie is well and truly out of the bottle. As it was
with GPS etc.

It is possible to slow him down though. You write the rule that no data
(nor voice) is allowed from ground to cockpit and no data other than
required for SA / safety between pilots.

Yes, this is virtually impossible to police but if the penalty was a 5 year
ban from competition, it may still work.

Jim