Rebooting the Realms... hmm.
1st: I'd use the new movie because it looks like it's going to be awesome. It would become the basis of the new realms. The humor, the tone, the style, the NPCs. If you want to sell a new Realms you need to sell it to the audience of that movie, because it's going to be bigger than the D&D community currently is, I'm fairly sure. Especially younger new Realms players.
2nd: Erase a ton of 4e's complications, break the whole Abeir-Toril thing down to make things easier for newbies. If Abeir ever shows up in the game from that point going forward, it's practically a 'shadow world' of Toril.
3rd: Hire a bunch of young modders who are hopeful for experience to "Remake" Baldur's Gate 1 and 2, plus expansions, Icewind Dale, plus expansions, Ruins of Myth Drannor, Neverwinter 1 and 2, plus expansions, using the 5e Baldur's Gate engine. They're eager to do it and you can release the whole thing as a "New Realms Bundle!" to make a ton of cash off material you have lying around and the elevation of community members.
4th: Focus on the Sword Coast (I know, I know) and Inner Sea regions. The Sea of Fallen Stars is a big story-point that will resonate with your audience, so making it and the Sword Coast into your main focus keeps the reality of Thay on the fringe of well documented territory in the "New Realms". Thay can be the mysterious mystical enemy just beyond the edge of what is known, letting your playerbase develop their own ideas of what NewThay actually looks like.
5th: Slowly explore additional realms as entire books. Do a Spelljammer release of a 64 page adventure, a 64 page player's guide, and a 64 page DM's Guide to the specific realm once or twice a year as both bundles and stand-alone options. Yes. I know that sounds ridiculous. But sell the 64 page Player's Guide to Shaar as a standalone at a lower price point and make the other two options only available as part of the 3 book bundle. You'll sell more total books that way as there are a TON of players uninterested in DMing...
... For now.
6th: Slowly expand the world to focus not on powerful allied NPCs but threats. Yeah, Elminster still exists. He's old and powerful but for REASONS he's a Patron, not a Force of Nature. What are those reasons? NEVER EXPLAIN. Same thing for the rest of the powerful NPCs and stuff. Drizzt? He's young again! Seriously, I don't care when the books were written. Drizzt is a 5th level ranger. He's got his cool swords and Gwenhywharf and whatever, but he's only been doing this all a short time with Wulfgar, Cattie Brie, Bruenor, and Regis.
7th: Mithril Hall is not the seat of the Dwarves, it still needs reclaiming. Just massage the timeline to push everything back, politically and socially, to the 1350s/1370s and call it whatever year the movie references. Consistency? THIS IS THE FORGOTTEN REALMS DAMN IT. There is no consistency.
Those'd be the big ones, I think.