Maybe it's an unpopular opinion lately, but I actually like the Forgotten Realms setting. However, every time I start a campaign set in the Realms I see myself going back to the Old Grey Box. The amount of lore current FR has is overwhelming, and I think it would benefit from a reboot (soft or not).
My idea for a FR reboot: Remake the Grey Box. Reset the calendar back to 1357 and publish a new campaign setting box set with information about the Sword Coast, the Heartlands and the Savage Frontier. Add some new stuff to it, like tieflings, to align with the lore of the new editions. Then fill it with interconnected plot hooks, like the old Grey Box.
So, how would you reboot the Forgotten Realms?
(Note this is a (+) thread, so assume that you're on board with rebooting the Forgotten Realms (even a "soft reboot") and focus on how to reboot it, not whether it needs to be rebooted)
Basically, you don't want to reboot the Realms, you want to
remove all of the damaging reboots. TSR and later Wizards kept coming up with stupid cataclysms to create in-game justifications for the changes in rules / classes etc that happened between D&D editions.
1st to 2nd Ed. If you've ever seen the 2ed Realms Adventures book (Female Paladin riding a Unicorn) the contents are basically a giant set of monkey patches to the Setting in book form (a whole Chapter on class updates, and another chapter only on the introduction of Specialty Preists (i.e. Strongly Domain Tied Clerics) for the whole pantheon. The Avatar series of novels was the longer and more convoluted story of how a bunch of Gods tramping around Faerun murdering each other is responsible for all the 1E->2E changes.
Similarly, the whole Spellplague was the justification for the changes required by going to
D&D 4E, and was WotC's excuse to toss anything they wanted out of the setting, smoosh all the planes and gods together, add some new scary big bads, and move everything else around.
They did it again with the "Second Sundering" which was the transition to
5E. WotC was trying to basically claw back in the direction of the original realms by tossing back in what they had tossed out ( and vice versa ) during the Spellplague. They also said the Gods aren't able to just show up again anymore ( essentially banning another Time of Troubles). Having basically reversed the 4E changes, and having made 2E-like changes harder to do, it seems that WotC had maybe learned its lesson?
Basically Wizards had in the end figured out what you did, that Greenwood's original realms are more interesting and have more space for adventure without the pointless bolted-on aftermarket cataclysms.
Cataclysms are not per se bad: see Dragonlance for a well integrated cataclysm that has human protagonists, and well examined consequences instead of revolving on deities faffing about breaking things to squish the setting into new game mechanics.
I personally think that taking a setting and screwing around with story to justify mechanical rules changes is just an outmoded idea. Just hand wave edition changes or retconn the minimum needed (it was always like this). This is part of the maturation of the hobby. Most fans now understand it's the stories at your table that count, and the goal of an RPG setting is to be evocative while leaving blank spaces for play. The final goal is not to create a dense 4000 year timeline of faux-historical canon that people can try to out-nerd each other by memorizing.