“For some, there is even an IRS tax on your exit. You pay tax on all your income every year. The Exit Tax is like an estate tax on the gain in your assets, even though you are not actually selling anything. It is the IRS’s last chance to tax you.”

• Renounce U.S., Here's How IRS Computes 'Exit Tax', Forbes, 27 Feb2017

Renunciation and tax compliance are two separate issues. See this post at Isaac Brock about interactions between Dept of State and IRS.