4 letter pronouncables and even 5L pronouncables will keep gaining value through the years. They have yet to reach their full potential, that is for sure.

4L acronyms that have good meanings will also go up in value.

Some really good brandables will continue coming from these short domains.

I think that there are still going to be quite a few letter combinations that maintain a reasonably low value in the future, but I still think that value will be above reg fee, at least for 4L.com