I dislike this "common purpose" concept and I hope it will never find its way in EASA world.
It's a can of worms.
I want to be able to legally fly my daughter to her home in Great Britain even though I have no other interest in going there but letting her reach her destination. Same thing with a friend who would ask me to drop him/her in a place where he/she wants to go.
Of course, I don't ask any payment from them and I make sure they know and agree that I can cancel the flight until the last minute before departure.
If someone introduces "common purpose" in Europe, it will put those flights in a grey area.
However, I totally agree with the proposal that, in case of cost sharing, the pilot must at least bear a pro-rata part of the direct costs.
The only way to put commercial flying with a PPL licence to a stop is to ensure that the pilot looses money when doing such a flight.
To limit the pernicious effect of internet sites like Wingly, it would suffice to state that publicity for cost-sharing flights is only allowed if the destination and date/time of the flight is pre-decided by the pilot and indicated in the advertisement. Any internet site that tolerates advertisements breaking this rule would be fined.