A "meta-argument" against all future arguments for God's existence ?

[R00tKiT]

Assuming is not knowing.  You can assume that is what God did but you don't know that's what he did as he may have had other ideas. 

You can play this game all day long about God having some hidden agendas, instead of looking at what God purportedly did and said. There is a principle called credulity, we assume things that appear to be so as indeed so, otherwise, we simply depart from reality.

In fact, we know he left certain backdoors in our reasoning by which it could be corrupted so as to allow the hardening of hearts.  

the 'heardening of hearts' verses you're alluding to only concern people who knowingly reject the islamic message, not people who made honest mistakes in reasoning, but I think you already know that.

 And Satan rules on earth, 

Show us the verse in the Qur'an that asserts that, I'll wait.

In fact the Qur'an asserts the exact contrary:

"Indeed, Satan’s schemes are ever weak." (4:76)