Actualy, pary is a waist of time.
Why should we pary, wait the animation, and then nothing happens, while we just can boom boom, next ?
Parry is an amazing skill moove. Make it great again.
It should result in an automatic and fast front stab aplying critical damage, with invulnerability while front stabing.
And if you think it’s to much strong, reduce the “pary moment” for make it harder and stylish.
That’s how pary should feel and be : Great ! 
Do you think they might add more stats for parry in the future? Like you said — for example, reducing i-frames but increasing damage after a successful parry
not necessary add more stat but make it an interest to try to parry.
Actualy, just while the animation time of the parry on an “enemi” , i kill 2 ones.
And i don’t speak about the time to attack then after parrying.
Pary is to much slow for the actual speed of the game.
So i will not say how they should do, it’s their game after all, and their own vision of it.
i just ask that if they want us to parry, to make it interesting to do better than just rush and kill without parying at all because it’s just more fast and simpliest ^^
Thomas has stated that Parry will be getting some work. To make it more relevant and more satisfying.