Perhaps this will, instead, just become another way for flying schools to advertise trial flying lessons
I think this misses the point a bit. Flying schools can perfectly legitimately advertise trial lessons any way they like from Wingly to an national TV ad campaign.
The ONLY thing a private pilot can legally use Wingly or Skyuber for is to advertise a genuine cost sharing flight that they are already planning to do. If they cross that line, they can and should be done for it.