If JDK 10 takes another 3.5 years, I think there’s a decent chance it will have Valhalla. If it comes out next year, not so much.
(It was not clear to me whether the faster release schedule for Java was meant to suggest multiple minor versions, e.g. Java 9.1, 9.2, etc., or “full” releases such as 10 and 11.)
Regardless, I don’t think opaque types and value types have quite the same goals, and I think opaque types still provide significant value even in the (hypothetical) presence of value types.