kbd now provides 'a' vlock, and since kbd is required by systemd, I had to replace community/vlock with kbd. However, the vlock provided by kbd has fewer features. Specifically, it lacks the option to create a new VT automatically, which makes vlock a perfectly fine X-locking tool. I used to be able to do vlock -a -n and it would switch to a new VT and lock everything. Unlocking would return me to X. Here are the options of the "proper" vlock:

-a,--all
Lock all console sessions and disable VC switching.
-c,--current
Lock the current session (this is the default).
-n,--new
Switch to a new virtual console before locking all console sessions.
-s,--disable-sysrq
Disable the SysRq mechanism while consoles are locked. This option only works if the -a,--all option given.
-t,--timeout <seconds>
-h,--help
Print a brief help message.
-v,--version
Print the version number.

I don't know why this "new" vlock is included in kbd and why it lacks the features vlock has had for years, but it's problematic. I guess either the new vlock should be part of kbd, or another package needs to be made for it. I don't know how these conflicts are normally handled... In any case, community/vlock cannot be installed on an up-to-date system anymore.

Here's someone else with the same problem:
https://bbs.archlinux.org/viewtopic.php?id=156308