you still have to pay exit taxes on renouncing, so not clear this is a good way of avoiding tax.
Also, forget about coming back (say for a friend's wedding or an important medical procedure), the laws assume that high net worth individuals are leaving to avoid future taxes.
excerpt[1]: If the Department of Homeland Security determines that the renunciation is motivated by tax avoidance purposes, the individual will be found inadmissible to the United States under Section 212(a)(10)(E) of the Immigration and Nationality Act (8 U.S.C. 1182(a)(10)(E)), as amended.
EDIT REPLY to : "Would they have to prove intent?"
Probably not because granting admission into the USA of a non-citizen (ex-citizen) is at the discretion of the Executive Branch of government and doesn't go through "due process" of any court system. So no "burden of proof" required.
[1] https://travel.state.gov/content/travel/en/legal/travel-lega...
Someone who is worth $15B would be very well-advised, and if he's been thinking about doing this in the past, his advisors may have decided that now is the right time to pull the trigger. Also helps to have plenty in the news these days, to avoid becoming 'the story' on a slow news day/week.
(https://www.irs.gov/individuals/international-taxpayers/expa...).