But the Double Irish (and similar structuring) is no longer permitted and would be treated as an illegal tax scheme today. (It's grandfathered in for companies already using the structure.)

Generally, between BEAT, GILTI, global transfer pricing policies, and the rise of nationalist economic policies, it's now riskier and more expensive to switch to a global corporate structure than to just keep everything in the US.

I used to do a lot of outbound structuring work, and now (post TCJA) almost everything is inbound, compliance, or restructuring existing foreign operations to more tax-friendly foreign jurisdictions (i.e., moving out of China to Vietname, etc.)