It's not a firm indication of what might happen with the game going forward, but there are some positive signs that can be drawn.
The classification board has revealed that it will be giving Breath of the Wild an M rating, which shouldn't really come as any surprise to anyone. But just for thoroughness, here's the full shot from the Board:
Developers typically submit games for classification when they're either feature complete, or very close to that stage. Nobody can say anything firm about what this means for Breath of the Wild appearing on the Switch.
It also wouldn't be the first time a game was classified well ahead of release. The Witcher 3 was originally classified on December 4 2015, having originally been slated for a release that month. But it initially got delayed to February, and then the week after the Board announced their rating the game was bumped again to May 19.
Nintendo could always do the same thing. But generally it isn't a case of adding new features or fixing up the story at this stage. It's usually major bug fixing, optimisations and giving the game the polish it deserves.
Thanks, Ryan Smith!