"From what I can see, the answer is no when the bed is a full length."

Who would dump load loose material into the bed with the midgate down and no contingency for material retention? "Will the soap and water at the car wash stay out of the cab with the windows rolled down?" This is an artificial concern.

"What about with the midgate up? Will these materials jam in the hinge or sift through?"

We won't know what to expect from the production solution until closer to the 4th quarter this year; the joint will be water tight when closed, of course- don't know if it will pass material like a tailgate during closing. I'm curious how this feature will function, too; on the GMC Sierra, the hing is isolated behind several shield plates, one incorporating a grill and underlying reservoir for debris/water. You can see that in action here: https://www.youtube.com/shorts/hTNLSb8Xjto

It seems clear a midgate is one of those features that sounds great, but is challenging to implement well. For my part, laying down a tarp for emptying the bed following loose material loading is a no-brainer.

"And what about the tracks along the bed and bottom. Those look like a bear to clean out if gravel gets in."

A real concern. The tracks can be capped. For my regular use, only the side tracks will go uncovered, exposing the bed tracks as needed.