I'd guess that the only reason it hasn't happened yet is Khaled has other things on his TODO list which take higher priority.
Exactly. No matter how much anyone might want a certain feature, Khaled puts things in based on whatever priority he chooses. It was stated many times in this thread and others that it is on his to-do list. As it hasn't yet been done, it's probably a low priority for him. As mentioned, the percent of users who 1) want encryption, and 2) would use mIRC's instead of a third party if it was available in mIRC, is VERY small. There are many more feature requests that have a much stronger support and would affect a much larger number of people. Those are the features that should have a higher priority. Throw in the fact that was mentioned of various third party options that work great already and it is going to drop even further in priority. Until those are taken care of (and if no other requests come in that also deserve a higher priority), I have a feeling this will remain low on the list.
The point most have been making is that regardless of whether or not it's a useful feature that some would really like to see, there are many more features that are even more useful and affect more people. Most of those who aren't posting in "support" of this wouldn't mind if it was added. They're not saying it shouldn't be added. Instead, if you read the posts, they're just explaining that it's not likely to happen soon and that there are some good alternatives in the meantime. We can't know what Khaled's plans are for upcoming features, but just as you said in your post about guessing... we can make a fairly informed guess that it won't be soon.