I think we are going to have to agree to differ, at a minimum for me to regard something as an edition change to PHB and DMG would have to be replaced with some significant changes. Colo's and Mordenkainen's going out of print while the basic rules of the game is defined by the 2014 rule books is not an edition change.Nothing is stopping me, and I am and will continue to use the older material, houseruled as I see fit.
On DDB, WotC has begun moving content that they have replaced (including the entirety of Volo's and Mordenkainen's, among a few other things) into "legacy" content that in the next few days will no longer be available for purchase. As far as they're concerned, that is clearly a direct replacement of content (and in some cases a removal of such). There is no reason to believe that WotC won't follow suit with AL and eventually physical product, including the 2014 core books when they get around to replacing them.
That of course doesn't have to affect whether or not a particular person or group can use that content, but it is a clear indication of WotC's intentions, and where they want the community to go.
Now if a new PHB and DMG are printed in 2024 that can be legitimately called a new edition but if I and my player can play characters from the 2014 book along side I am not going to be bothered.
It we cannot then we will consider the changes at the time and whether or not to follow them.