Still working, folks.
Good news: I have a working version under iOS 11.4 and below now uploaded to the App Store.
Bad news: I have to update all the screenshots that go into the App Store page and write all the update copy, and then we have to wait on Apple to review the whole business and post it.
I have no idea how long that takes these days. Used to be at least a week or so, but that was back in the day, and this is an update and not a brand new app, so things may be different.
I'll keep everyone posted.