I'm not saying it will but that it could. Part of me thinks that the changes we are seeing will be scaled back due to negative feedback and not be as many big proposed changes that we have seen so far in the playtest material.
But if the level of changes (or something close) that we are seeing go through, the game will be changed quite a bit. It will still have the same basic structure/mechanics but there will be limits to how much mixing and matching can happen between 5e and 1D&D.
Currently you can't use the more powerful Races from 5e (which provide Ability increases) with the Backgrounds from character origins playtest (which provide Ability Increases and a feat) and pick a Class from 5e with a subclass from 1 D&D (or vice versa) that have a different number of subclass features at different levels. And yes they cover the ability score increase in a sidebar and can make conversion rules for other things. But freely mixing and matching will through off the balance of things.
But with the amount of changes we are seeing (if a similar amount make it into the final product) I know there will be groups that don't change to the new rules and am sure there will be groups that will abandon all the old rules and just stick to just the new. Other groups may use a houseruled mix of the 2.
It is possible this with will create a divide in the community where some people are not buying the new material that is being produced by WotC and maybe even being supported by some 3rd party publishers that stick with 5e.
So while there is certain to be a divide, how significant do you currently think it will be? It might only be a small number of groups that don't convert to the new rules and stop buying any new books from WotC. Just like with every edition change some groups will remain with the edition they are used to/like. But will the size of this 5e only community be significant? Could the divide be big enough that 1D&D actually, ironically, creates a need to make a new 6e to reunite the community? (Probably not?)
And with the changes you have seen so far, if they all pretty much make it into the finished 1D&D release, would you and your group change to the new version? What are your thoughts so far about this?