If the United States were to apply the Reed Amendment against Saverin, it could lead to a constitutional challenge someone who has the pocket change to pay to for one. This could also result in a challenge of the constitutionality of the HEART Act provisions, i.e., the current exit tax.
The other problem with banning Saverin for life is this: He’s a billionaire and the world is a big place. How is this going to hurt Saverin? But it will be a big message to the world that the United States is not the place you want to go if you want to do a business start up. The United States will only hurt itself if it decides to be vindictive towards Saverin.
Renunciation Guide has a good primer on the subject of the Reed Amendment (here and here). There are serious issues of fairness and constitutionality. Above all, the Expatriation Act of 1868 makes it clear that the United States officials must recognize Eduardo Saverin’s right to expatriation as a fundamental principle of the government (based on the language of the Declaration of the Independence). To punish Saverin with a ban from entering the country would thus violate Saverin’s right to expatriate.