Is it possible to open an exported JSON file in arcweave?
Unfortunately this is not possible.
The main reason the exported JSON cannot be imported back to Arcweave is that this export does not keep layout information (e.g. the x, y coordinates of the elements on the board). The primary use case for this export is to be parsed so that your data may be imported to the game engine of your choice.
We may implement another export that could serve as a backup (could be imported back to Arcweave). However, we are also planning to create a 'history' feature which could prove more useful in terms of backup saving.