I had a similar idea on WP's idea lab a few years ago: Allow previewing protected pages. SD0001 suggested that it had already been declined by devs on the grounds that it would be confusing to newcomers, but I don't buy that because we can show sufficient warning before they can preview it. Nardog (talk) 07:35, 25 January 2023 (UTC)[reply]
Newcomers are a very important user group for us, that we are trying to accommodate as much as possible, so it might very well be that we decide in their favour. I do understand the thought of the wish though, it can be helpful to understand the template code. KSiebert (WMF) (talk) 10:54, 25 January 2023 (UTC)[reply]
Note WikiEditor is already loaded on protected pages where CodeEditor is loaded (example). I imagine it would be a relatively simple flip of a switch. The absence of the "Publish changes" button already communicates the situation quite clearly, and, more to the point, I fail to see how loading of WikiEditor could affect newcomers' ability to understand it. Nardog (talk) 06:29, 26 January 2023 (UTC)[reply]
Not sure why syntax-highlighted wikitext would be more confusing to new editors than non-syntax-highlighted wikitext. I'd worry about performance implications though - CodeMirror can be quite slow for large pages. --Tgr (talk) 02:23, 1 February 2023 (UTC)[reply]
Support Syntax highlighting is such a key part of learning to do something (even if it's just looking), that we should enable it for beginners. I do not think it signals that a page is editable. Femke (talk) 19:07, 10 February 2023 (UTC)[reply]
Support but better to allow previewing changes to a protected page. Use case: check whether my proposed fix to an article or template actually works before submitting an edit request. Certes (talk) 21:20, 10 February 2023 (UTC)[reply]
Support Often the most complicated templates are the ones that are protected. One can use syntax highlight for simple, not protected templates, but can’t for complicated, protected ones? Doesn’t make much sense from a user viewpoint. Tacsipacsi (talk) 19:50, 13 February 2023 (UTC)[reply]