I suspect that the low profile flush rails were designed more for esthetics and aerodymanics than for actual utility. The rails on the '14s are identical to the ones found on the '11-'13 models.
I would agree with this assertion. It is obvious that starting in 2011, aerodynamics ruled all decision-making at Jeep (Chrysler? Daimler? whatever) with respect to the Grand Cherokee. As well as all other platforms, except the Wrangler.
Thule and Mopar (which I think was a rebadged Thule) made cross-rails that did attach directly to these flush rails up untill recently. It only seems to have been w/in the past year that they've stopped making them. I have hear rumors that the mounts were failing at highway speeds when loaded with large cargo boxes or full baskets. These are still just rumors though as I've never seen a news article about this or a forum post from someone who experienced this. However, in today's litigious society just one incident could lead to a lawsuit that would make everyone run for cover.
If that is the case (and I'm not saying it isn't), I would expect the Rail Grabbers to be discontinued, as they truly attach directly to the rails as well. The only ones that have been discontinued are the ones that (apparently) conveniently attached to the rail without the screwing clamps of the Rail Grabber, or the screw-in mount method of the K624 fit kit. The Rail Grabbers rely entirely on the integrity and stiffness/strength of the rails, and truly are held TO the rails by a piece of metal that hooks under the inboard edge of the rail, but only covers an inch of rail at the most. The beefy looking portion of the Rail Grabber mounts are simply sitting ON the rails; they take none of any tension load, and the only shearing load they resist is through the friction of the rubber feed of those mounts.
The Yakima and Rhino decision to use the bolt holes that normally hold the flush rails to the jeep's roof as mounting points for their rails is pretty clever. At the very least it makes the flush rails look like they're doing something and not just there for decoration.
Pretty clever, I agree. The only thing I worry is by removing those screws, and either replacing them with the threaded shaft (Whispbar K624) or reusing them with the bracket (Rhino Rack), you have broken the water-tight(?) integrity of the rail-mounting to the roof. Just how well do those mounts resist water intrusion after the install?
Also, with the Whispbar, you're pretty much looking at a permanent installation, as there doesn't seem to be any provision for removing the load-bars unless you leave that threaded shaft in place and sticking up (best I remember from looking at the install instructions). At least with the Rhino, the bracket is screwed to the roof, then the towers to the bracket, and it even has a cover available for when the load bars are removed.
I'm beginning to think, as I typed the above, that the flush rails of the Grand Cherokee likely AREN'T the problem, but the head-sheds at Yakima and Thule. Rhino has taken the Yakima Whispbar mount idea a step further in convenience and utility. It really seems to me that Yakima has dropped the ball.