The change in question has already been reverted (Nightly 8.1 Changelogs - 2024 - #82 by system; n.b. 8.1.41 was changed to a hotfix release so the changes mentioned will be live in 8.1.42), but it was unlikely to (deliberately) affect you anyways. The warning was only intended to show up if you accessed the date formatter inside certain Vision components (e.g. popup calendar) from an asynchronous thread. All scripting in Vision is automatically on the EDT unless you explicitly invoke an asynchronous thread, so it's very unlikely you would even have noticed that aspect. However, our code turns out to very much access these components on asynchronous threads (e.g. in find and replace, or during template repeater construction) so we reverted the change anyways, because it's impossible to distinguish between those different cases.
I would definitely recommend postponing your upgrade until 8.1.42 is available to avoid the nuisance warnings in the designer, though.