It's almost like WotC came to the conclusion that continuous concern about Forgotten Realms "canon" is a waste of time and energy and they just want to tell people to go ahead and use the 30 years of documentation they already have to create whatever type of FR game they want and to stop worrying about trying to run a cutting-edge "current" game.
They got tired of trying to invent three paragraphs of new Turmish history for every edition and just want to you use whatever Turmish stuff you have lying around for your upcoming Turmish campaign.
What I want isn't new canon at all--I want the Eberron treatment where the official version of the game stays put on a particular date so you can use all the material how you want.
Of course that ship has long ago sailed, but they could have done it with 5e instead of this awkward mess. As it is, it's a chore using 5e material because they make it externally look a lot like the pre-4e era I use, but in reality it isn't and they interweave all sorts of later stuff into it. This means I have to know (look up) even more stuff about what was and wasn't true in the old FR so I can figure out how to use the new books without screwing up compatibility with my library of previous work that fits together much better with itself.
They say that the current version is effectively timeline neutral, but you have a new Waterdeep map with different areas, different movers and shakers in the world, parts of Faerun that have been replaced since the 1e-3e era, etc.
If I we're going to fix it I'd declare a few different points in the timeline as fixed starting dates. New products would have to be able to be set in any of those dates, based on preference. They would have to include information for what varies by starting point, such as NPCs and political conditions. The best bet is not to set anything around the regions that have massively changed. They could even have the current mess as the default starting point. They might need an appendix for how to set it at each starting point, abs would likely need sidebars throughout. Better yet, pick whichever starting point fits better for each adventure and make the adaption material go from there.
Things like, "If you are playing in starting point A or B, the dragonborn Darcus Dracarian is replaced with the human Damian Drakefield. His dragonborn honor guard is instead composed if humans and half-elves." Or, "If you are playing in starting point D, the Open Lord if Waterdeep is
__, instead of
__. Rather than encourage the PCs to X, they will insist they do Y, but will offer a 3,000 gp reward if they do. They won't help or hinder the party if they choose to ignore them."
Or for something more appendix worthy, "If you are playing in starting point A, Blingdenstone isn't recovering from a previous fall, it's been a thriving community for centuries, and the effects of the demon lords' invasion are a subtle cancer that has begun to infect it. Make the following changes."
"If you are playing in starting point B, Blingdenstone only recently fell. When the party arrives, they find a group of svirfneblin attempting to retake it from oozes and wererats. The following scenario describes how this might play out, and what Blingdenstone might look like based on the results."
That sort of thing. A new campaign setting, if produced, should probably take a different approach than previous ones, by having its goal be laying out the various starting points. Describe what makes each unique and why you might want to play there. Explain which overall things vary, such as deities, regions, organizations, racial dynamics, magical access, etc. Present each starting point as a mini-setting in other words. Heck, do this (imagine a bunch if subsections it multiple chapters in these divisions).
1. Introduction to the Forgotten Realms
2. The Realms as it always is
3. Era 1: The Classic Setting
4. Era 2: Wake of the Time of Troubles
5. Era 3: Legacy of the Spellplague
6. Era 4: The Second Sundering
7. Customizing content for a different setting
7.1 Approaches to adaptation
7.2 Comparison if differences
7.3 Reference tables
8. Appendix A: Published products by era and region
Etc. Some of what I stuck at 8 would just be interwoven throughout. In the section on a particular era, when describing the Sword Coast, or Calimshan or whatever, along with describing what it is like at the time (focusing on the distinctive ekements that weren't already covered in section 2) you would say which products to get for a more in-depth source on the era appropriate material on that particular region or concept.
Section 7 would compare and contrast themes and details (in detailed discussions, as well as table summaries), so you can read a brief timeline of the afterlife, as well as look at a table that lists which gods are active/available in each era.
This is just what I can think of laying in bed messing around on my phone before getting up for the day. The concept is totally doable, and makes the FR more user friendly for fans of all eras.