Will never happen. They can always scale it back, but in a few years the teams will find new ways to exploit the rules and gain pretty significant downforce.
Fatter tyres on the other hand is something that's been talked about quite frequently, even amongst drivers. I can see a shift towards mechanical grip happening over the next few years, but nothing as radical as the recent rule changes for the next 7-8 at least.
I think everyone's forgetting this brilliant season is going to be ruined at Abu Dhabi anyway, but whatever.
I'm against gravel too. Aint nothing wrong with decent grass though, high-qualify shit that minimises the risk of digging in and rolling.