I think it all ends up being a bit of a no-win scenario.
Avoid change, and the fans have no reason to buy your books because they already own the material.
Embrace change, and the fans get upset that you changed things.
Undo change, and the fans who liked the changes get upset that you changed things back.
This also describes WotC's unenviable position regarding the D&D Next rules as well. Pathfinder/legacy3e/OSR/OGL is the 'avoid change' option, 4e was the 'embrace change' option, and now they are facing anger from people who liked 4e at undoing those changes and people who like previous editions wondering what 5e can offer that previous products haven't already covered.
All I can say is that I bought the 3e Dragonlance campaign setting book after having read the Weis and Hickman books and felt utterly gypped that I was reading rules that had almost no resemblance to the world Tanis and Raistlin adventured in.
I say let the novels advance the timeline when narratively appropriate, and the rules follow suit; the fact that they're doing it backwards seems silly to me.
Dragonlance is a prime example of repeated retcons/WSE's changing a setting to the point that it's no longer recognizable to the people who actually liked it. I bought some 3e Dragonlance books, but only to support running games set before the 'present' date of the setting, which I ignore in both my games and my personal life (seriously, my wife recently got into reading the novels, and when she asks if there was anything written set after the Legends series, I'm just telling her 'no')
I have to admit I have conflicting feelings on this sort of thing.
On the one hand, I tend to dislike advancing of timelines and so on. Leave that to individual DM's. I largely buy setting products to mine for ideas, but if I do intend to play in one, I'd just as soon pick it up and be able to use it easily with older products.
On the other, new editions do tend to introduce new stuff. And surely some accommodation has to made for the new stuff in settings they plan to continue selling... within reason.
'Within reason' - there's the rub. I think trying to introduce dragonborn into the Realms was a mistake. Or at least it was a mistake by bringing them in with yet another RSE. Better for them to have been lower-key... maybe they were a long-lost sarrukh experiment, or from the same world as the saurials, or something.
Trying to introduce major new stuff into a setting that had no place for it up to now is a very dicey proposition. It can be done - I myself am quite satisfied with how I wove sorcerers into a homebrew world of mine - but it is very easy to do badly.
Much better, if you want a world that has the kitchen sink along with everything else, is to just build the setting from the ground up to contain it all. We might all have been better off if 3e and 4e (and even 2e!) had simply brought in new settings to showcase their rules, and provided conversions of the old settings without trying to shoehorn in stuff that didn't exist at the time..
But on the gripping hand, that's a lot of work, and thus a lot of money. I'm not sure there really is an ideal solution to this sort of thing.
Can't XP you Shadow, but you summarized a lot of my feelings on this topic. However, I'll go a step beyond what you said and say that I think that attempting to shoehorn new content into old settings is pretty much always a mistake, particularly when you push that new content into the foreground of the setting and have to make major changes to the lore to accommodate it. If a single player in my FR campaign wants to play a Dragonborn character, that's fine- he's a mysterious traveler from a land beyond who is making his way in a strange world. I don't want Dragonbornopolis suddenly springing into existence as the capital of Dragonbornistan, along with major institutions devoted to training classes and power sources that never existed before. The coherency of the setting starts to fall apart. In some cases it seems like a new edition is churned out just to say 'hey, you can play this cool new class/race in the setting you love.' No one really needs a complete rev of the setting lore to receive that permission.
I always prefer when settings are designed from the ground up with certain races, classes, etc., in mind. Dark Sun is a good example of doing this well, as was Dragonlance before the 3e-era books made a mess of it. There were no half-orcs, no gnomes, goblins, etc. in Dark Sun. Period. The lore established that these races had either never existed, or had been destroyed early in its history. There were no orcs on Krynn, and clerics only existed pre-Cataclysm or after Goldmoon and the Companions returned knowledge of the gods to the world.
So to the OP's point- I want to see sandboxy settings that say 'here is the world in its 'classic' form (2e for Forgotten Realms, 3e for Eberron, 1/2 for Dragonlance, 1e for Greyhawk), this is the default date, things develop however you want them. I would be OK with there being multiple eras of play- a book for pre-Cata or post-Cata Dragonlance, for instance, like Sovereign Press did. What I don't want is to adopt the White Wolf model where the world meta-plot moves forward with or without me, and favorite settings or NPCs pop in or out of existence according to the plan of some developer somewhere, and all the new supplements are set in the 'present' as the setting marches forward in time. Most settings never get a lot of breadth of coverage- a few key nations or portions of the world get fleshed out, and the rest is ignored. 2e went a little broader since it was around for so long and built pretty seamlessly on 1e without the need for WSEs, but there were still a lot of basically blank spots on a lot of maps. I would rather see those filled in with interesting story ideas and adventure sources than have the world timeline be advanced in published adventures I may or may not ever play.
