Well, what if all this talk of a reboot is just a marketing move? Maybe this game will fit PERFECTLY in with Lament of Innocence? The casual gamer who haven't played Castlevania before will buy the game because it doesn't require any knowledge of previous games, because the other games haven't happened yet. Hardcore CV fans, on the other hand, will immediately be able to connect it to the IGA timeline. And so everyone is happy. No harm done.
Konami really wants to broaden the appeal of Castlevania, so they decide to make a game that takes place before all the other games, which doesn't really reboot the series, but gives new players a chance to experience Castlevania from the very beginning, while also giving the hardcore fanbase a new beginning. Konami obviously calls it a reboot to get more players interested. Possibly. Maybe. Dunno.
Only problem here is if Dracula shows up in LoS. That would contradict rather badly with LoI. Though if Dracula isn't in the game, I don't see why they couldn't connect this to the canon timeline, and still attract new players by simply lying to their faces while they're hyping the game. And if LoS turns out awesome, I'm sure everyone will forgive Konami. Heck, the casual players will never even know that the game was connected all along, if they have no knowledge of the series whatsoever.