Are core devs discussing this possiblility of a large scale infiltration and how to avoid?
Actually the best way to take over Bitcoin, imho, would be to get a few agents become core devs, respected (and influential!) members of the community.
Then they can take whatever decisions they want, from blacklisting you to putting your IP into the transaction or whatever surveillance ideas they could have.
Many people would even agree to it, when they read, that Al-Baghdadi is using Bitcoins to transfer money to his international fight club and there is a need to change some parts of the code, that is EXCLUSIVELY being used to hunt terrorists. Since I am no terrorist and I have nothing to hide ... go along. I know you are protecting me.