I think some sort of warning might still be useful - the checks are still experimental in nature, and the chances of a false positive higher when in suggestion mode. So the original reason for adding a warning still applies.

I'm taking this off the sprint board for now.

Reasons:

1. Per what @Esanders shared above, and @Sdkb, @Quiddity, @DLynch have named offline, there is value in reminding people who have the Suggestion Mode beta feature enabled that the feature is, well, in beta. People might forget that they enabled the feature and/or hold memory of having done so in the case of people who have the Automatically enable all beta features... setting turned ON.
2. There is also value in having a way to communicate that certain suggestion types are experimental in a future where Suggestion Mode is enabled as a default-on feature and we are iteratively releasing new suggestions that are at varying levels of "fidelity" / "maturity"

To be discussed: might there be a clear, intuitive, and non-intrusive way we could label experimental checks that's less blatant/jarring than the current red text that also affects the page layout (especially so on mobile)?

Change #1248501 had a related patch set uploaded (by Esanders; author: Esanders):

[mediawiki/extensions/VisualEditor@master] EditCheck: Only show experimental warning in experimental checks

https://gerrit.wikimedia.org/r/1248501

Change #1248501 merged by jenkins-bot:

[mediawiki/extensions/VisualEditor@master] EditCheck: Only show experimental warning in experimental checks

https://gerrit.wikimedia.org/r/1248501

Per offline discussion, we've decided to make it so the current warning only gets presented alongside Checks/Suggestions that are classified as Experimental:

I've filed T419156 for us to consider iterating upon the current red text warning to something a bit, mmm, more pleasant while still remaining effective at communicating that a given suggestion is experimental.

With the merged patch each experimental check now gets this within itself: