I have upgraded the forum.
From the outdated template notice in the admincp dashboard, there is only 1 template sometimes merge successfully but sometimes not that is footer template where they (vbulletin) added a new hook. {vb:raw template_hook.footer_copyright}

So for old customers, I can advice that you can upgrade with no problem from previous vb4.1.11 version, no problem.
This vb4.1.12, I can say is not a major styling update version like vb4.1.10.

I will update my collection in 2 days.