Can you clarify what you mean by this? What does it being opinionated have to do with there being a URL you can share?
When you open a repo on CodeSandbox, you automatically open the main branch (e.g. https://codesandbox.io/p/github/codesandbox/test-sandbox/mai..., which is the main branch of our test repo). To contribute to this branch, you can click "Branch" in the editor, and we'll automatically create a new branch, and redirect you to the URL of this branch.
They key here is that you can share this branch (with anyone who has access to the repo). If someone else opens this same branch in CodeSandbox, they will join the same workspace as yours and see your cursor. This allows you to share in-progress work with your team more easily, because you're sharing a link to a branch. When someone else opens that link, they will see a running environment instead of static code, even if you're not online.
So you could essentially say that dev environments on CodeSandbox are multi-user, which is a key difference compared to other cloud environments. With other cloud solutions, the link is tied to your personal environment (so the link is only valid as long as you are online). With CodeSandbox, the link is tied to a branch, which can be shared and opened any time by multiple users.
A totally separate question if, I may: Does the editor support using keymappings from other apps? In VS Code, for example, I can use (it may have been through a plugin) JetBrains (IntelliJ/PyCharm) keymappings which is really helpful because I could essentially feel like a pro in VS Code immediately, despite not having used it before. Can I do something like in Codesandbox?