Fair enough, the whole SI-2712 debacle is indeed a source of issues well beyond Spark but in general it's just a matter of adding a compiler flag to sort it out. The other example is of course the whole mess of macros...

On the other side though, strict backwards compat creates it's own set of costs (that are often harder to quantify. Java backwards compatibility is great but it seems like it is also at least prat of the reason Java moves at such a glacial pace.