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SurveyJS
Open-Source JSON Form Builder to Create Dynamic Forms Right in Your App. With SurveyJS form UI libraries, you can build and style forms in a fully-integrated drag & drop form builder, render them in your JS app, and store form submission data in any backend, inc. PHP, ASP.NET Core, and Node.js.
What I'm imagining is a plugin which embeds neovim in the add card and edit card text fields, just like glacambre/firenvim works. I think for this to be useful the text which you'd edit would need to be the one you normally edit in a text field, not the raw html code. Although if this is too hard to achieve a lot could be done with neovim itself to make it user friendly.
Have you seen AnkiVim or External Editor? These solutions don't embed vim/neovim but you still can use it to edit fields.