I can’t comment on what Twitch’s plans are for VIP going forward. But the way it is in it’s current form is that if you’re a mod, you’re already beyond that of a VIP as you have access to everything a VIP does and MORE. All you’re missing out on is a purple icon.
Many of the suggestions by streamers that lead to this VIP status is that they wanted to be able to more clearly indicate certain users in chat, but without giving them moderator powers. As a moderator, you already stand out in chat AND have moderator powers.