You are confusing two different ideas here. The Canvas format is MIT licensed in the same way that Markdown uses a BSD-type license. That means we are giving explicit permission for anyone to use the format and build apps, scripts, plugins on top of it.
This is a pretty grating response, given how pointed it is. It's not made any better by the first sentence; it seems that you are the one confusing two different (types of) things:
> The Canvas format is MIT licensed in the same way that Markdown uses a BSD-type license.
In no sense are these two things comparable. "Markdown uses a BSD-type license" is a true statement because "Markdown", in the context where it makes sense to say this, is a Perl script—a program, licensed in a way that is not uncommon for open source programs to be licensed. Your canvas format is not a program. It's a 70-line TypeScript interface definition, going by your own link:
To call this "open source" (let alone open source "in the same way that Markdown" is) is a very odd choice. It's less odd for anyone who recognizes that it follows a common pattern, where folks with something to sell often openwash what it is that they're selling based on the (not unfounded) perception that having it be thought of as more open than it really is tends to confer certain positive benefits. It's why Steve Jobs lied about FaceTime being an open standard, for example.
Whether or not you're giving any explicit permission to build apps, scripts, plugins, etc. is largely moot—to be frank, you don't have the power to dictate otherwise. On the other hand, if you're saying that you're aiming to steward and participate in what (you hope) turns out to be a vibrant ecosystem built on a common format, then that's cool. But say what you mean, though. Calling it an open format or an open standard would be fine; "open source", however, this is not.
I appreciate the distinction you're making. I could have been more accurate in my description. Markdown states in its own documentation that the name refers to two things, and "Canvas" to date fits mostly in (1)
> Thus, “Markdown” is two things: (1) a plain text formatting syntax; and (2) a software tool, written in Perl, that converts the plain text formatting to HTML.
What we have done so far is shared an open spec for the .canvas file format, with a type definition that helps developers understand how to create properly formed Canvas files. We also are giving permission to people/companies to use this format with the freedoms that come with the MIT license. In addition we're also putting forward the intention that there should be a free and open format for this type of canvas data, with some similar properties to Markdown. Perhaps in the future there will be more open source tooling fitting into definition (2).
The goal here is simply to help people feel more comfortable that the canvas files they create are their own, and can eventually accrue longevity as more tools get built around the format. I hope this will lead to a rich ecosystem outside of Obsidian. We're committing to keeping it an open format, and hope to collaborate with other people who might want to adopt it.
The same can't be said about the PSD format, so I do think there is a difference in the level of openness that we're aiming for.
Photoshop/PSD on the other hand is a closed proprietary format: https://en.wikipedia.org/wiki/Proprietary_file_format