You are aware over time the physical media distribution model will be going away in favor of an all digital media model or even a no media streaming only model. Just like VHS, BetaMax, LaserDisc, DVD, and HD-DVD before it; Blu-Ray will be phased out in favor of new technology. Which is in this case digital media and no media streaming only models. Samsung the leading producer of Blu-Ray players will no longer be making new Blu-Ray players. There was even debate whether the new gaming consoles would include an optical drive to play Blu-Rays. They did this time around but don't bet on it for the next models in a couple years. And studios have even started offering digital releases of their films, and producing less physical Blu-rays.
So I wouldn't bet on Mulan automatically coming to Blu-Ray, it may, but don't be surprised if it doesn't. Also I wouldn't be surprised if you don't see Mulan on the subscription side of D+ until April or May of 2021.
Point is the future is being written now, and Disney is one of the authors of that future. Mulan is just the first domino to fall, more will come. And you can bet other studios will soon follow suit.