Perhaps Hoffman might be exiting soon and Julie is being considered?
Believe me, Jackie would ONLY leave a paying gig for another paying gig. She knows she's a hard type to cast and works when she can work. Get them coins, girl.
It probably has more to do with the understudy being much, much younger and wanting that part to land better. I don't know why they'd want to pay for this when they're already bleeding money.
I was wondering if maybe they were doing this in case Jackie Hoffman needed to be out a little longer than a week (maybe her injury will take longer to heal). We don't know what the nature of that injury is and it may keep her out an additional week (they likely want her back for awards season so I'm guessing they want her to rest up).