Oh, it’ll almost certainly come to the iTunes Store eventually, along with all the other distribution channels (rentals, BluRays, HBO, etc.), there’s no reason for them to shut down those other channels and millions of reasons ($$$) to keep them around.
You're not really buying the movie here. You’re buying the digital equivalent of a movie ticket, which allows anyone in your living room to watch the movie as many times as desired, for as long as you subscribe to Disney+. Yes that’s different than most of the circumstances surrounding a normal movie ticket. They’re trying to figure out how to make all of this work, in this new pandemic world.
And, effectively, what you’re buying is access to watch the movie as many times as you want (while subscribed to D+), up until they release it for normal streaming on D+, likely 6-12 months from now (after it’s worked it way through rentals and BluRays and all the other mediums). After it’s released for general streaming, 6-12 months from now, you’ll still have your ticket, but the ticket won’t matter, because anyone with a D+ subscription will be able to stream it for no added cost. So, what you’re really buying is early access to unlimited streaming.