For me it's the missing Jupyter support that's preventing me from switching
This would unblock people to write their own Jupyter integration for example, or whatever else they want. There's load of cool stuff like Argus https://github.com/cognitive-engineering-lab/argus that rely on creating buffers with custom UI, and Flowistry https://github.com/willcrichton/flowistry that rely on graying out some code, and I want this stuff on Zed too
Their extensions API is still a bit lacking, but Jupyter support in the style of vscode should be possible with the current capabilities.