The 24-105 glut happened when the 5D MkIII was (for a time) unavailable as body only. The only way to get one was to buy it with the 24-105 kit lens. That dumped loads of 24-105s on the market. If Canon continues to produce the 24-105, I'll be surprised. But I've been surprised before.
I can't wait to see some real world tests on this 24-70 f4. The Digital Picture side-by-side comparisons with the 24-105 IQ will be especially interesting.
"I know rocks. Rocks are hard."