The timeframe of migration for a specific wiki is pretty vague, partially because of potential complications in the migration process, if there are problems when migrating a wiki, "a few weeks" still holds true. My estimation would be to have it migrated in around 2 weeks, but there is a big chance it could be earlier or later. In terms of testing, there is the sandbox wiki where you can do that.
You have our sympathies... which wiki is this?
The Delicious in Dungeon Wiki - it's fairly small so I understand why Fandom's moving it now, but it would be nice if some of the bigger bugs outlined here were ironed out before moving wikis onto the platform.
You're right, the Animanga footer works! They must have fixed CC transclusion which is very nice.
#3 and #4 might be known issues. Otherwise it is good to hear the transition was relatively smooth.
One thing you might not have noticed is that the content area for the page is narrower when you make you window wide compared to the legacy wiki version, which is annoying, but not awful.
On a side note, I hope Delicious in Dungeon gets an anime adaptation. Similar stuff like Restaurant to Another World and Isekai Izakaya got adaptations, so I don't see why Delicious in Dungeon shouldn't get one.
The content area looks cramped because it is smaller in width. I've looked at legacy and UCP wikis side-by-side.
Have you seen Elfen Lied or Goblin Slayer? Violence and gore never stopped an anime adaptation. It could be the author's wishes that may be preventing an adaptation, but that is unusual. Also, they supposedly already did an anime commercial, so the author wasn't opposed to that.
That's true - I haven't seen either of those but am aware of more violent anime than Delicious in Dungeon would ever be.
The only reason I think the author might not be interested in an anime adaptation is that she seems fairly private and might not be someone who is interested in the level of publicity that an anime generally brings. The commercial, however, really does tease the potential for an anime adaptation, so we can hope!
Notifications for non-UCP message walls will not be added. Fandom sees it as a waste of time to incorporate that feature into UCP since all wikis will be converted to UCP and thus, eventually, there will be no non-UCP message walls to get notifications from. That was their logic behind not having it for Discussions and that was 4+ years ago.
They are only temporary in the sense that there might be a newer skin or version in maybe 10 years time, but there is no way to go back to the old version. Just like DeviantArt, Twitter, or Facebook, platforms have to update every few years, and now Fandom is also doing that. It may not always look the best, but if you really want to wait for a next big update, come back in more than 5 years and hope for the best.