Before:
qemu-system-x86_64 -cpu ? | grep EPYC
x86 EPYC                  (alias configured by machine type)              
x86 EPYC-IBPB             (alias of EPYC-v2)                              
x86 EPYC-v1               AMD EPYC Processor                              
x86 EPYC-v2               AMD EPYC Processor (with IBPB)

Upgrade:
...
Setting up qemu-system-data (1:4.2-3ubuntu6.7) ...
Setting up libgfortran5:amd64 (10.2.0-5ubuntu1~20.04) ...
Setting up libubsan1:amd64 (10.2.0-5ubuntu1~20.04) ...
Setting up python3.8-minimal (3.8.5-1~20.04) ...
Setting up gdbserver (9.2-0ubuntu1~20.04) ...
Setting up language-selector-common (0.204.2) ...
Setting up build-essential (12.8ubuntu1.1) ...
Setting up libpython3.8-stdlib:amd64 (3.8.5-1~20.04) ...
Setting up python3.8 (3.8.5-1~20.04) ...
Setting up python3-lib2to3 (3.8.5-1~20.04.1) ...
find: ‘/usr/lib/python3.7/lib2to3’: No such file or directory
find: ‘/usr/lib/python3.7/lib2to3’: No such file or directory
find: ‘/usr/lib/python3.7’: No such file or directory
Setting up qemu-block-extra:amd64 (1:4.2-3ubuntu6.7) ...
Setting up libcc1-0:amd64 (10.2.0-5ubuntu1~20.04) ...
Setting up liblsan0:amd64 (10.2.0-5ubuntu1~20.04) ...
Setting up mdadm (4.1-5ubuntu1.2) ...
update-initramfs: deferring update (trigger activated)
Created symlink /etc/systemd/system/mdmonitor.service.wants/mdcheck_continue.timer → /lib/systemd/system/mdcheck_continue.timer.
Setting up libitm1:amd64 (10.2.0-5ubuntu1~20.04) ...
Setting up bolt (0.8-4ubuntu1) ...
Setting up gcc-9-base:amd64 (9.3.0-17ubuntu1~20.04) ...
Setting up libgcc-s1-arm64-cross (10.2.0-5ubuntu1~20.04cross1) ...
Setting up libtsan0:amd64 (10.2.0-5ubuntu1~20.04) ...
Setting up libatomic1-arm64-cross (10.2.0-5ubuntu1~20.04cross1) ...
Setting up python3-distutils (3.8.5-1~20.04.1) ...
find: ‘/usr/lib/python3.7/distutils’: No such file or directory
find: ‘/usr/lib/python3.7/distutils’: No such file or directory
find: ‘/usr/lib/python3.7’: No such file or directory
Setting up libgomp1-armhf-cross (10.2.0-5ubuntu1~20.04cross1) ...
Setting up liblsan0-arm64-cross (10.2.0-5ubuntu1~20.04cross1) ...
Setting up libgomp1-arm64-cross (10.2.0-5ubuntu1~20.04cross1) ...
Setting up qemu-system-common (1:4.2-3ubuntu6.7) ...
Setting up cpp-9-arm-linux-gnueabihf (9.3.0-17ubuntu1~20.04cross2) ...
Setting up libgcc-s1-armhf-cross (10.2.0-5ubuntu1~20.04cross1) ...
Setting up qemu-system-mips (1:4.2-3ubuntu6.7) ...
Setting up libpython3.8-dbg:amd64 (3.8.5-1~20.04) ...
Setting up libtsan0-arm64-cross (10.2.0-5ubuntu1~20.04cross1) ...
Setting up qemu-system-x86 (1:4.2-3ubuntu6.7) ...
...

After:
qemu-system-x86_64 -cpu ? | grep EPYC
x86 EPYC                  (alias configured by machine type)              
x86 EPYC-IBPB             (alias of EPYC-v2)                              
x86 EPYC-Rome             (alias configured by machine type)              
x86 EPYC-Rome-v1          AMD EPYC-Rome Processor                         
x86 EPYC-v1               AMD EPYC Processor                              
x86 EPYC-v2               AMD EPYC Processor (with IBPB)                  
x86 EPYC-v3               AMD EPYC Processor

Marking as verified.

@Markus - if you could give this a better test on your systems with the respective HW as well that would be awesome.

P.S. as expected libvirt can make use of EPYC-v3 but not Rome yet.
$ virsh domcapabilities | grep EPYC
      <model usable='no'>EPYC-IBPB</model>
      <model usable='no'>EPYC</model>