On the workflow navigate action, add a check box to “open in new tab”, and if possible a condition when to open in the new tab.
Mockup below of the dialog;
Being able to open new tabs programatically, rather than on user action, is going to be tricky to justify.
As it is usually going to look like Spam.
I think Emmanuel had said something about this in the past not working well with pop-up blockers unless it’s explicitly coming from a link element. I could also be making that up, as it’s just before 6am here in DC