As long as there is enough clearance between the two screens to add a temper glass screen protector to each.

Every phone I've had with a case, grit collects betweeen the case and the back of the phone and scratches the phone up. I can imagine the same thing happening between the two screens if folded in my pocket.

Eh I'm not too interested in multitasking on my phone. Even on my 12.9 iPad Pro multitasking is mediocre. If I want to be productive I simply go to a laptop or desktop.

Clamshell phones let you close your phone completely, and have been around for a long time. Actually, are they still a thing?

So Clamshell Android phones are a thing. The Freetel Mushashi is a T9-style Android phone with dual touch screens on either side.

Samsung has the Android W series phones which have a similar format.

Regarding the sibling comment, after the Droid 4 and the Motorola Photon Q, there has been a drought of physical keyboard landscape slider phones. Portrait sliders have been available for the Blackberry Priv and KeyOne/Key2, but aside from the soon-to-be-released Fxtec Pro1, not much landscape slider android phone action is going on.

last mainstream device i can recall in this form factor was the droid 2? I think it's been a while since a major one was released, but I could be wrong.

Only problem is I like messaging in portrait mode, but watching things in landscape. Kind of kills the benefit for me.