Unless all Audax events become mandatory route with GPX validation, then the possibilities for cheating are always there.
But for most people, we don't really care.
Someone else cheating does not invalidate my ride, although it may devalue it somewhat.
The only people who care are those few in contention for awards.
So my general position is that we probably should not make it more onerous on everyone in order to satisfy the few.
I'm not sure the 50% rule actually works.
The basis of it is that on a cal event, you are 'with other people' who can validate your ride.
I don't think that's actually true.
Typically on a longer ride, we set off in a big group, we thin out, and then group / split / re-group in different groups along the way.
Every rider who temporarily teams up with another will assume they have ridden the distance.
Plenty times, they will ride for a few hours and not even get their name.
I often see people for a while, and never see them again.
There is no one person who can say 'yes, he rode the whole distance'.
Would the org put out an e-mail to all entrants asking "Did some dude in an Audax Ecosse top ride with any of you, and where?"