Randy updated the ZDoom.org website a few days ago concerning the future of DECORATE and the current ACS code. Here's a snippet from the original post:
Q. Why create a new scripting system when you already have ACS?
A. Because ACS is extremely limited, and it is better to start with something new than try to extend it. Maybe we'll even see a new scripting language for maps that can make up for ACS's shortcomings!
For more details, visit the ZDoom.org website.