Technically you can use Shortcuts to set whatever icon you want but it takes some effort to set up. And I don’t think it can use transparency so it’d have to take up the whole square (or out more effort into making the background of the icon match your background). And it’ll take a second longer to load the app as it goes through Shortcuts first
Shortcuts do not behave exactly like the default app icon when it comes to animations, notification icons, and so on, and they create a redundant duplicate icon. It's not as big of an issue now that there is an app drawer on iOS, but it's still less than ideal.
There's still no justification as to why an user shouldn't be able to control how things appear on their screen - a developer doesn't get to choose what I see or not see.