While there are existing tools like journal-viewer (github.com/mingue/journal-viewer), which uses WebKit, I found that its GUI doesn’t integrate well with the Qt/Plasma ecosystem.
I was going to bring that up. I’ve never heard of journal-viewer, but I have used:
GNOME Logs
KSystemLog
QJournalctl
You mentioned specifically integrating well into QtPlasma, what improvements do you hope to have over the native KDE KSystemLog?