> Would it be pragmatic to add a "custom icon" option for questions to make them more distinctive in the nav bar?

They already do!

If you find the right room :). I've added icons to a few — basically those I expect will get chat traffic for years rather than days/weeks:

* https://topanswers.xyz/meta?q=1  
* https://topanswers.xyz/databases?q=30

Feel free to post suggestions for other long-lived question rooms (like this one?) as answers here — I've subscribed to this question so I should see them.

I'm not sure this is a good idea. Already the "real rooms" (top level room(s) belonging to sites) are being drowned out in the bar by the somewhat less important and transient question rooms. I would almost argue that all question rooms should just have a solid color (matching their parent site theme) with no icons at all, or that the identicon should be dimmed out or tinted or something so than the rooms with _REAL_ icons stand out more.