Trello boards export to JSON, would you consider it open? OneNote notebooks are also an open and well-documented specification, as well as local first and backed by a very reliable company, which makes them just as open as Obsidian by those standards.
The Canvas JSON is not an export format, it is the file that the app actually reads and edits. Being explicitly MIT licensed also gives permission to other people/companies to build their own tools using that format.
OneNote and this canvas format might be equally open and interoperable, but it's a hard claim to justify that onenote notebooks are as open as a folder of mostly standard markdown (the two exceptions being wikilinks and embeds)
I peeked at the onenote format standard [1] and the obsidian canvas standard. The difference is hilarious. The onenote standard is painfully complex, provided as a .pdf, and binary to boot. Compare to an example obsidian canvas - this is obvious, text-based (I could read it with notepad++) and easy to understand just by reading it:
{
"nodes":[
{"id":"6c711bf8c24c4f5b","x":-226,"y":-62,"width":400,"height":400,"type":"file","file":"testin/2022-10-14.md"},
{"id":"4dd7d04cdd0b379c","x":-530,"y":-209,"width":250,"height":60,"type":"text","text":"this is a note"}
],
"edges":[
{"id":"0c589a4d6bbb06aa","fromNode":"4dd7d04cdd0b379c","fromSide":"bottom","toNode":"6c711bf8c24c4f5b","toSide":"left"},
{"id":"eda9f3edb3ec232a","fromNode":"6c711bf8c24c4f5b","fromSide":"top","toNode":"4dd7d04cdd0b379c","toSide":"right"},
{"id":"abf404722ba48c3b","fromNode":"4dd7d04cdd0b379c","fromSide":"top","toNode":"6c711bf8c24c4f5b","toSide":"right"}
]
}
https://learn.microsoft.com/en-us/openspecs/office_file_form...