That already happened in Germany - https://qz.com/666871/german-viewers-of-immigrant-hating-you...
"To target immigrant-hating videos, the room-sharing service uses keywords on YouTube’s ad platform that are associated with far-right content and anti-immigration groups, such as Pegida, Germany’s anti-Islamist group, and its leader Lutz Bachmann. Other keywords include “refugees out” (“asylanten raus”), “refugees terrorists,” and “the truth about refugees.”
A German can’t watch a anti-immigrant YouTube video associated with a keyword without first seeing a 30-second preroll ad from Refugees Welcome."