My issues begin after login. Something is sourcing ~/.bash_profile which contains my ssh keychain init:

/usr/bin/keychain ~/.ssh/id_rsa
. ~/.keychain/slackware-current.dhcp.ldev-sh > /dev/null

Prior to the big merge, I used a script that had the above and had it autostart as part of xfce4 init.
As best as I could tell, ~/.bash_profile wasn't being sourced during X11/xfce4 init hence the need for
the script to be run from xfce4 autostart. I removed the reference to the script from xfce4 autostart,
but that didn't stop the behaviour. I then commented out the keychain lines from ~/.bash_profile, tried
a login, and that worked. Also tried logging in via ssh first, going through the keychain init, then
logging into X, and that too worked.

Something about invoking ssh-askpass is preventing the display from showing. I'm wondering if $DISPLAY
is set when ssh-askpass is called. I don't see any cli request for passphrase in any logs.

You should start a new thread as your issue is not the same as mine, where you can provide a subject line better suited to your specific problem, and your issues won't be confused with the ones I'm experiencing. We'll both get better help that way.

So here's what I've found, and to summarize. I run XFCE in initlevel 4. I also load ssh keys via shell init using the keychain program.
My .bash_profile includes these lines for keychain init:

Prior to the big merge, I had a script in .config/autostart that ran the above.
Since sddm seems to source ~/.bash_profile, and I didnt have SSH_ASKPASS set, ssh-add
just hung there, and no way to provide the ssh passphrase to ssh-add.
After much testing, I found I no longer have to have the script in autostart, and I had
to add to .bash_profile.
Now when I login, I get x11-ssh-askpass prompt for passphrase, as it was before, and my
X session and terminals all share the same ssh-agent, as it did before

Marking as solved.

Thanks to those who tried to help, and I apologize if I wasn't clear about the problem.

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