Probably not what you had in mind, but you can already style individual options in a dropdown using the stylesheet:
Either using nth-of-type or nth-child to target the option based on its index,
or using its data-label property to target it depending on its label.
There's also probably a way to style the modal this way.
Now, it's not as simple as built-in properties, but it would allow you to do it right now.