I suspect you’re right, but if they don’t do it until the new stuff is announced I suspect the price hike would drown out the news of all the new stuff. And I really don’t think Apple wants that.
If they announce it on, to pick a date, July 1 then by the time the iPhone is announced it will be somewhat old news. It will still get mentioned but it won’t be the main feature of every story at announcement time.
Like so many other companies Apple is between a rock and a hard place with this stuff.