They want to play in a current ever growing world because it allows their characters to either be a part of it...
No it doesn't. Not a single thing a player does in any DM's Forgotten Realm campaign game is reflected in the official story of the Forgotten Realms. So no one is ever actually a "part of it". Rather, they are the protagonists of an alternate universe Forgotten Realms.
...or witness those changes happening.
And this also isn't true, because by the time you play in a FR campaign, the book has already been written. The changes have already occurred, none of which came from anything any of the players did. EVERY change happened because the authors of the products made something up.
The only time any FR player could suggest they actually had a part in the "official canon" of the Forgotten Realms are the few times WotC has run some of their Epic convention adventures where what happened at most tables got actually incorporated into the official story. But that's the only time. Anything else has come from the minds of the writers of the material and that's all.
Look, I can understand the desire to have a setting book that is "current", because it feels like time going forward is open to you, and thus you can play in your game and not contradict anything (because there's nothing in front of you to contradict.) But in truth none of that matters. Whatever you do in your game isn't contradicting ANYTHING, because your Forgotten Realms isn't "real".
So you can play Tyranny of Dragons (which is now currently "in the past") and there's quite possibly a chance that Tiamat actually shows up and rampages across the Realms. And your Realms campaign will have to deal with that. But... in truth it never "actually happened". Because it didn't happen in the "official canon". And thus insisting you need an "official canon" setting book so you can set your game there is pretty much pointless. You aren't playing in the "official canon" and never will.