Thanks for all the input, everyone. Even though it’s beginning to look like the situation is pretty hopeless. 
FWIW, I agree:
$ rpm -qil libvdpau1
...
This package contains the libvdpau wrapper library and the libvdpau_trace
debugging library, along with the header files needed to build VDPAU
applications. To actually use a VDPAU device, you need a vendor-specific
implementation library. Currently, this is always libvdpau_nvidia. You can
override the driver name by setting the VDPAU_DRIVER environment variable.
$ rpm -qil libvdpau_nouveau
…
This package contains the VDPAU state tracker for Nouveau.
So despite what “libvdpau1” says about “this is always libvdpau_nvidia” I’m assuming the rest of the description is correct: It’s a wrapper around the actual libvidpau implementation which in my case is “libvdpau_nouveau”, which in turn is needed for GPU video acceleration.
So as much as I’m out of my league disagreeing with @mrmazda, I’m leaving both “libvdpau1” and "ibvdpau_nouveau” in for now.
Very interesting information about X startup, but I don’t think nouveau is getting past the kernel “oops” and to that point. /dev/dri isn’t created at all, much less anything underneath it like in my nomodeset/“nouveau isn’t running” boots which have:
$ ls -AlRF /dev/dri
/dev/dri:
total 0
drwxr-xr-x 2 root root 60 May 24 13:34 by-path/
crw-rw----+ 1 root video 226, 0 May 24 13:34 card0
/dev/dri/by-path:
total 0
lrwxrwxrwx 1 root root 8 May 24 13:34 platform-simple-framebuffer.0-card -> ../card0
Note that’s one more proof (if any is needed) that nouveau isn’t running.
Thanks for the suggestion. I tried removing it (zypper also removed kernel-firmware-all) but it made no difference.
Does more than remind me “a little bit”. This looks to be exactly the same problem.
That’s what I’m going to do.
BTW, I tried nosimplefb=1from @suse_rasputin’s other thread. That didn’t help (same nouveau crash/hang), plus it made the boot message console scrolling flickering and very slow.
I’m going to comment on this in my next post.