Ello ello, I just want to quash any worries you might have.
Us announcing the deprecation of the Legacy Java Client won't have any impact on RuneLite, which is exactly what Adam says himself in that screenshot ("which is not that they are doing right now"). In our blog we've tried to be as clear as possible with that in the first sentence of the section:
"Finally, let’s talk about what these plans mean for the Legacy Java Client – and to clarify, we’re talking about our own official one, not RuneLite or other third-party, Java-based clients."
We love RuneLite, most of us internally use RuneLite, and at the end of the section we even say that RuneLite is one of the alternative options they should use:
"Soon, you’ll need to play via the Official Client, RuneLite, or HDOS. All three clients can be accessed in the Jagex Launcher, which requires a Jagex Account."
Finally, the team will still be maintaining the Java client for the sake of RuneLite and HDOS as we know it's important for them and for all of you that use them.
Hopefully that all helps!