The thing that still makes me question if this game is another direct sequel to OoT is the fact that there is another Hyrule Castle sitting right there in the distance which doesn't fully match up with current theories. I can see two scenarios right now for a 100 years post OoT game. One feasible, but still iffy, the other just doesn't work.
For both the way things looks is that at the end of OoT in the Fallen Timeline Link was defeated. Zelda and the Sages fought to seal Ganon away in the Sacred Realm and the Sheikah took Link into the Resurrection Shrine to heal.
In scenario 1) Zelda and the Sages succeed in sealing Ganon away on their own. Peace returns to Hyrule for a time. Enough time that they could build a completely new Hyrule Castle/Town far north of the old city. Possibly the Temple of Time and old city were also rebuilt a little, as evidenced by the Eastern Abbey, but it was clearly not the same as before OoT events. Then at some point Calamity Ganon breaks free. Struggling to contain him the Sheikah send out their Guardians to help, but Ganon someone how takes control of them. The guardians then lay waste to the kingdom and almost completely level old Hyrule and the Temple of Time, but something stops them. Likely Zelda and the Sages having contained Calamity Ganon within the new Hyrule Castle somehow, but they could not reseal him in the Sacred Realm. All in all many years would have to pass between the Link's defeat and Ganon being sealed by Zelda and his eventual breakout for all this reconstruction to occur.
In scenario 2) Immediately following Link's defeat at the end of OoT the Sheikah send out the Guardians to help contain Ganon now that the Hero has fallen but he takes control of them and goes on a rampage across Hyrule, leveling what is left of the already devastated Castle Town and trying to demolish the Temple of Time. Zelda and the Sages though still manage to seal him away before things are completely overrun. The problem here though is where did that entirely new castle up north come from for Zelda and the Sages to contain Calamity Ganon in? A giant castle doesn't just pop up out of nowhere.
Scenario #1 seems far more likely, but in both instances how is <100 years, likely significantly less so for scenario #1, enough time for the whole Kingdom to seemingly melt away and for the old Castle Town area to become mythologized as the Old Man states that Legend says the plateaus is the origins of the Kingdom of Hyrule. Dude looks old enough that he, if not the very least his parents, were alive to see Scenario #1, if not #2, unfold. Just feels off, but then again Nintendo has never really been one for clear and precise accuracy and logic when writing out Zelda games. So it's still all entirely possible it's a direct sequel to OoT.
Another issue for Scenario #1 at least is that the Old Man clearly states that Calamity Ganon appeared 100 years ago and then Zelda tells Link he's been asleep for 100 years. 100 years is pretty precise language compared to just saying a century which provides more wiggle room. So that makes it seem like the arrival of the former caused the slumber of the latter. Which would make sense for Scenario #2 that every transpired immediately after Link's defeat in Oot, but then we are back to the issue of where the hell did an entirely new Hyrule Castle come from and why was Ganon sealed there and not in the old Hyrule castle region and around the ToT.
Now alternatively this new Hyrule Castle could be the Northern Palace from LoZ/AoL. As LoZ and especially AoL map don't fully match up with previous games they might be retconning the shit out of all that, taking elements from both, which can kind of be seen in the BotW map from the 2014 demo. So in this scenario the Great Plateau would be the Old Hyrule of OoT, which happens to be near Lake Hylia, somewhat matching up with LoZ map which had an elevated area to the N-NW and the graveyard area, Easter Abbey? Then just like AoL much further north is the Northern Castle, what we see as likely Hyrule Castle and Calamity Ganon in BotW. Major changes are the reduction of large waterways from AoL into simple rivers and Death Mountain being in the NE corner of the map and not the Western middle. What can you do. Nintendo's never been afraid of jacking up geography.
Anyway. BotW could then take place after AoL. Despite preventing Ganon's resurrection and awakening the original sleeping Zelda at the end of that game, somehow Calamity Ganon breaks loose in the Northern Castle shortly after. The Sheikah come out of the wood work to help contain him, but the Guardians get taken over and run wild. Link get's wrecked and Zelda uses the Triforce, or something, to contain Ganon in the Northern Castle. Cut to 100 years later and the game starts.
To me this makes more sense for the Great Plateau to become mythologized as the birth place of Hyrule Kingdom as that would be many hundreds of years after OoT and not just <100. As well it would better match up between the 100 years of Calamity Ganon appearing and Link being asleep and such. Then again it might be too much time given the condition of the ToT and all the events that occur between OoT and AoL. Similarly there are other issues. Such as there are technically two Zeldas at the end of AoL which I guess they could just ignore but that is kind of weird situation.