So, to see a UAT equipped aircraft with a 1090 receiver you need to be close to an aircraft with 1090 in/out. Most reliable way to do this is to put adsb 1090 in/out on your glider.

To be seen by that UAT equipped aircraft, same answer.

With adsb out on the glider and the flarm core 1090 rx, the only issue I'm seeing is latency in the ground relay system.

It will be really neat if a flarm core s/w upgrade adds UAT rx, or turns on all of the h/w in the box, especially the second flarm transmitter. Lacking that, instead of switching to a new flarm box, would it be better to put the money into adsb out?

That said, if I was adding flarm, the new one looks nice.