If people are already testing on 12.4 then there's no real need for a point release to activate this. I guess we'll know in a few weeks.
A few scenarios for 12.4.1.
The update was about more than just Apple Card (in fact Apple card was not even mentioned). Also you can expect Apple Card to be available by Monday, September 23 as they said Summer 2019, unless they send an announcement that its been further delayed. It seems they are more on track for early August but summer doesn't actually end until Sept 23 so anytime before that is within their announcement window.Everyone thought Apple Card was going to come with it right away and now Apple hasn’t said anything so I’m sure a lot of people could have done without the update. Who knows when we will see Apple Card.
They have addressed the issue by suspending the program. While they did say a future update will bring it back, I find it hard to believe that it'd be anytime soon. This is not something they're going to want to rush out the door.I would expect 12.4.1 to address the Siri privacy issues. Apple states that a future software update will sort this. Could be iOS 13 though. Worth a punt.