Whatever the tech ultimately used to achieve this, what will it do
to the sport? I know some people thought flight computers would
ruin the sport, then GPS, then moving maps, but thus far it is
still far from ruined. But visible thermals sounds like the
biggest step yet
towards reducing the challenge. What do others think?

I think it actually doesn't matter what people think. Technology
will become available for the masses sooner or later, which will
challenge both pilots and contest organisers to think outside the
box.

Pilots will have to deal with more (sources of) information, and
will have to prioritize.
Contest organizers must find new ways to challenge pilots.

Besides this, the question is if remote detection will change the
field a lot. The same arguments hold for this as for the discussion
about powerFLARM I think.

Personally I am an aerobatic gliderpilot (and there's no tech for us
at all!), so this doesn't affect me directly. The only advantage is
that I can probably glide further when I decide to go cross-country
one day.