Yep.
The only solution is to cover the tyres since fender has been rejected.
But again covering the tyres is against the nature of "formula1".
As you said is also an aerodynamic advantage covering they tyres.
Tyres are actually the biggest enemy for engineering since they make the air dirty around the car and wings has the job to deflate the air around tyres.
Now if they cover the tyres the air around them will be cleaner and a revolution of wings stats consequentially...
Currently full wet tyres is useless thing. If we have conditions for wet tyres, usually it means that we will have red flag. There is too much water on track and too bad visibility.
But we shouldn't be expecting for big changes. On TV broadcast our local commentator that Pirelli is working on new wet tyres. But it should be closer to current intermediate than current wet tyres.