Vincent,
After your post, I did a little investigating. Here is a presentation provided by a technical marketing manager that explains why ELS was started and all the changes made, thus far. According to Salman, ELS preserves EX and MX feature richness, consistent functionality (One Junos), and has enhancements as compared to the old CLI and performance improvements.
I am out of my technical area of expertise but wanted to make sure you were given information to address your concerns. I hope it helps.
Sue Leonard, Champion Program Manager.