Support used to be the lowest-queued role, so I imagine that's why Riot hard-coded it to support giving autofill protection.
If the numbers are showing that jungle is now the lowest-queued, though, it might be best for Riot to switch it. It's fully possible, given how much more attractive Riot's made support over the past couple years (Pyke and Rakan likely being the biggest contributors since they're flashy and shit, and removing sightstone probably helped a lot too).
I don't think having it automatically switch is a good idea, though. That opens it up to changes potentially happening too fast, at which point it's impossible to communicate it. Releasing a skin or even a different time of day could change what gets protection. Depending on your luck, it could change mid-queue.
Maybe if a role is the least popular for 3 consecutive months, it should become the protected role? That'd be enough time to indicate a full shift in preferences, rather than just a "Ooh shiny new skin" response.