Joining in here to support Speed2 - you can quite literally add in files to the base game that hook into files with no way to detect their changes if these changes are UI-related. And if you can detect them then it is some lua code that is doing the detecting, which can be easily removed too.
To hook into (hurr) your example on snipe warnings: correct me if I am wrong but as far as I can see you cannot make such a system. You can see what the UI can access from the engine at:
Searching for units in the sim (as your post suggests) is not part of that.
You can find all kinds of (interesting) UI capabilities when inspecting files in /lua/ui, of which some (indirectly) do influence the sim - such as pausing units or changing the priorities of units.
I do agree that there should be a discussion on whether we make some of the UI mods more commonly known, such as Advanced Target Priorities (ATP) (that even without CPU sniping can still have a major impact). More commonly known in terms of: users get prompted for the existence of the mods on their first launch of the client, there is some tutorial / guide that tells these mods exist and that gets prompted on the first launch or they are automatically downloaded from the vault on your first launch so that if you ever scroll through the list of mods, you'll see them in there.
I'm not sure how applicable this is (and how desirable), but I think the existence of these type of UI mods should be communicated somehow. Not knowing about / not using a UI mod like ATP does give you a distinct disadvantage in my opinion, which can feel unfair.