While I agree with part of your argument I don't necessarily think it applies to making elves more inclusive. This is a minor aesthetic change--not an alteration to their core concepts. Allowing them to have a greater range of features does not take anything away from people who view them as predominantly Caucasian. If elves belonged to one group, expanding it to others just means they have to share, as opposed to having it taken away from them entirely. No one is asking for more diversity to the exclusion of Caucasian features.
And D&D changes its existing, established identities with every new version of the game and updated source book. Just look at the tieflings. This isn't a inflexible franchise to begin with.
I also don't think creating new media is the answer to this problem, given how huge a property D&D is. Larian's answer to D&D is DOS and, personally, I couldn't really get into that world. I enjoy the world of D&D and in actual table top games we have the freedom to make our characters however we want. The line of thinking "If you don't like this one thing then maybe you should go elsewhere" is the exact kind of gatekeeping that I find so insidious, because it invalidates the feelings of people who otherwise DO love the world. (Btw, I don't think that's your intention--I'm referring to other posts and how others may use this logic to disregard the feelings of marginalized people.) Given that D&D IS a franchise that changes over time, clinging to certain aesthetic values while going along with other changes points to peoples' anxieties outside the game rather than a devotion to the immutability of the lore.
Another great post. I (quite literally) couldn't have said it better myself. I agree with all of this. The last sentence is especially on point.