In my project, I use exported tilesets in JSON format. But I've found two problems/bugs here. I'm using the latest snapshot version of Tiled.
The first one is with an exported tileset with terrain information.Once I click the 'Edit Tileset' button, the new tab opens with the tileset, and I can edit the terrain as I want. But the problem is when I save the tileset, both by ctrl+S and 'Save as', selecting .JSON extension: the file is saved as a .tsx file. Even when using 'save as', and selecting JSON as extension, the process will warn me that the file has a different file-format.
The second one is regarding custom tile properties. Adding custom properties in an exported tileset, by first clicking 'Edit Tileset', and then saving the file, overwrites to a tsx file, but keeping the json extension. In this process, the tileset is automatically embedded. Once I export the tileset again (as a JSON), the custom property is nowhere to be found in the file. And checking in the tileset editor, indeed the custom property is gone.
The first problem, seems not to happen when first embedding the tileset, but as explained, this can't be done with the second problem, since the custom tile property will disappear on exporting.
I hope this is clear, and could be fixed