Composite of Elon Musk and Bill Ackman.Chesnot/Michael Bezjian/Getty Images for Brand Innovators Billionaire investor Bill Ackman told the WSJ he would be interested in a deal with Elon Musk's X. However, he caveated that by saying he doesn't know if X is interested, or if the deal is doable. Ackman's Pershing Square obtained approval for an investment vehicle on Friday, targeting companies looking to raise at least $1.5 billion.