I was talking to Yrliet and here is a question. HOw the Imperium would treat a half Eldari? If the father a influential figure in the empire?
Depends who you're asking. The half-breed in question could likely pass themselves off as some sort of lesser mutant, which are common enough that it wouldn't raise eyebrows.
If people knew the truth, however, the most common response from most would be horror and that it's heresy. Nobles would possibly see a bargaining chip to gain influence over the father.
Inquisitors would vary, depending on their personal attitudes. More Puritan types would purge the half-breed, while others would see a useful tool in their dealings with the Eldar.
As always, it's better to not think of the Imperium as the monolithic entity the wargame presents it as, and think more like Dune, or any large polity: In the Halls of Power, the rules cease to matter.