A 'blind trust' would be for someone who has a portfolio of stocks, bonds etc. wherein the individual would not be able to use their knowledge to gain leverage etc.
There's no such thing as a 'blind trust' for a media empire, because everyone in the empire knows exactly who is in charge and who pays their salary. Patronage does not stop because of lack of communication.
Do you think that if Trump owned FoxNews, but was also President - that Fox reporter would feel totally free to investigate Trump on whatever terms they wanted? Knowing that he owns them? And can come back in a few years and end their careers?
No.
In fact, a media org. owned by a public representative might be likely do all they can to back him, cover up scandals, paper over ugly things, and prop him up. Then they would get big fat promotions and guaranteed career progress down the line. Among other things, such as possibly favorable treatment and exclusive access by the political regime.
There's no way to segregate a media empire from it's leadership temporarily.
As for 'illegal or not' - nobody knows the answer to that, because we don't know what Zuck wants to do.
Moreover - for the Office of Pres - it's unclear. Trump has an army of lawyers trying to determine whether it's legal or not for him to keep his holdings. Some are indicating that state use of Trump hotels is illegal. Some are indicating that having his children run the empire would be illegal. It hasn't been tested in courts, and the laws are unclear - for President.
But the legality if it moot: someone with massive control ownership of the media should not be able to hold public office, it's one of the most glaringly obvious examples imaginable. (Aside from someone in public office handing out contracts to companies they own directly.)
