Am I right that impairments can reversed for financial assets for the FV trough P&L 'cause as they are always measured at fair value no “real” impairment exist? (IFRS!)
An impairment is just a BS situation where fair-value and carrying value become disjointed. Writting the asset down removes the impairment.
With that said, you have to know the fair-value of the asset so be cautious with this assumption. I could see where a problem would provide information on a thinly traded equity or security and ask some tricky question about impairment of the financial asset.
Yup and only the existence of thinly traded assets or illiquid markets do not trigger an imparmaint. 
So therefore, FVTPL and held for trading securities do not have impairments becasue they are always recorded at fair value.