Frontline should be the casual mode. The stakes are always higher in CC because you as an individual player have much more personal responsibility than you ever will in FL, this is regardless of whether it's a ranked match or not. In fact, removing the distinction between casual and ranked would highly encourage players of all skill levels to take the matches more seriously overall. They should funnel players who are new to PVP into FL so they can learn the basics. They already basically do this by giving players a daily bonus for it, but they could do more. The basis of this thread is the fact that ranked queue dies, that's for a few reasons which are well documented. Higher ranks it's because people get their targeted ranking and then stop and there's no incentive to keep playing. Lower rank it's because most people who are really interested in playing ranked have already surpassed Gold tier and probably a lot due to the anxiety you're talking about.
No, I don't think if you collapsed to casual queue completely that ranked queue would die off, especially with the proposed change of linking ranking to job. It would have the exact opposite effect. I'm sure there are some issues it would cause, that will be the case with any change normally, but killing off the queue? I really don't see that being a problem at all. Casual players till need to get their wonderous tales done, they still want to fill out their challenge log. That's something no one ever really takes into account. All that kind of change would do would directly address the fact that lower tier ranked dies off, and plenty of other changes to reward structure could easily address higher tier ranked matches dying off as well.