install/51716: Can't install NetBSD 7.0 from USB stick on recent Apple machines

[tgl%sss.pgh.pa.us@localhost]

>Number:         51716
>Category:       install
>Synopsis:       Can't install NetBSD 7.0 from USB stick on recent Apple machines
>Confidential:   no
>Severity:       critical
>Priority:       medium
>Responsible:    install-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Dec 14 05:05:00 +0000 2016
>Originator:     Tom Lane
>Release:        7.0.2
>Organization:
>Environment:
can't help you on that because I don't get as far as being able to run uname
>Description:
I've tried to install NetBSD 7.0.2 on two different Apple machines: a late-2013 Macbook Pro and a late-2012 Mac Mini.  On both, the install gets as far as looking for the root device and then hangs up indefinitely.  I'm not the only one seeing it, because the exact same behavior is shown in this YouTube video:

https://www.youtube.com/watch?v=XbhSfo2YgXE

>How-To-Repeat:
1. dd NetBSD-7.0.2-amd64-install.img onto a USB stick

2. Insert stick into reasonably recent Apple machine

3. Power up; hold down Option (ALT) when you hear the startup chime

4. Select USB stick (it'll appear as "Windows", which is a usability fail, but let's keep our priorities straight)

5. Wait.

6. Boot process gets as far as

	boot device: <unknown>
	root device:

and hangs up.

>Fix:
I do not know a workaround.  End goal was to install NetBSD onto another USB stick, but I've so far failed at that.