Some might, but most won't. I didn't say that they would do the work to upgrade to UTF-8, and it's not even clear that it's desirable overall for them to do so. I don't think this is backwards at all - it is just the way of things. Old interfaces that work tend to get used with few changes for a very long time. The POTS telephone interface is ancient and very clunky, and we could do far better today.
ACE wins because it has the best backward compabtibility and the lowest barrier to quick deployment.