I don’t follow why this is unfortunate?
Personally, I think one of my favorite things about Java is that, all things considered, it's a small-ish language. So I'm glad that Java is both willing to evolve (slowly, letting other people try stuff out first) but also clearly focused on a curated feature set and resistant to letting new stuff in to bloat it. I am very happy to deal with minor things like no multiline string support if it means we get to avoid being a terrible mess of language features that ruby, scala, python, etc have accrued in a relatively quicker timescale.
I was fairly sad around the java 6-7 days where we went quite a long time with no visibly major new language features (diamond inference was 7's big thing, lol). So it is nice that we're moving a bit faster than that, now.
It will look something like this:
STR.”text with \\{variable}”, but anything implementing the TemplatedString interface can change the behavior of interpolation. There is not even a requirement to produce strings only!
I'm guessing Java hate, which is kind of fashionable. If Java evolves to stay relevant, it won't be usurped and fade away.
Long term this could lead to a loss of maintenance for tools and libraries for these languages which could kill them and leave those that migrated with a dead & decaying ecosystem.
Of course this is a bit of a stretch but it's not unheard of.
Silhouette is probably just because of one guy's schedule, but Play/Slick seems like after-effects of lightbend's layoffs many months ago, and while I don't know the cause of those it seems plausible it's because of the kind of thing you describe above.