Comment 8 for bug 1855703

It is my experience that, as soon as you enable issues on GitHub, no user will bother with launchpad anymore. More so if you don't advertise it on the website.
It's then a matter of taste of the core developers if the launchpad bugs need to be moved or not. I personally wouldn't bother with it. A move helps you get rid of launchpad right away, but can be complicated as you point out correctly. Fading it out seems much easier, and worth having to switch back and forth a little longer.