Sure. Then if they come out a new PHB that includes stuff from those books... it isn't a change to the core rules. It just adds to them.
And if those options make the original ones obsolete for rangers, well, then, so be it.
You could even include optional (aka improved) bonus action rules.
I think that this is a difference in terminology. Adding to the existing edition is, wait for it,
adding to the existing edition. In other words, it's still 5e. What I have been arguing about is against a 5.1, 5.15, 5.3 which would require changing an edition. Where something from before are no longer legal characters, etc.
We can and have been adding options and rules since the Elemental Evil players option came out with Genasi and spells and stuff. That's not a new edition, just new choices in the existing edition.
But you do bring up an interesting point - will they publish a 5e core books that includes some of the additions in addition to everything that is in there now. That's not as cut and dried.
Okay, speaking on keeping it 5e but adding to core books, I am not so sure. I would deem it moderately unlikely, but that leaves plenty of room for it to happen. And if it's going to happen, 50th Anniversary would be the logical time for it. Call it 60/40. The reasoning behind that is the core books are the gateway for new players, and having too many options, especially contradictory ways to achieve the same thing where one is weaker (a trap option) I don't think is something they will do. That gets to the interesting point of do they change the Starter Set (which means two starter sets might not be compatible with each other). It also touches on AL's PHB+1 a bit, but I hope that's not a consideration.
To sum up: I am still absolutely sure they will not advance slightly beyond 5e. "5e" includes what we have done so far - adding new options without expiring or replacing old, and issuing errata that corrects problems. They may turn the crank and come out with a whole 5.5e or 6e.
In terms of adding new rules material to the core books, I think it unlikely but possible. Adding new covers and other things that don't affect play I think are very likely.