Add SIMD, or streaming extensions, at least to JVM
On (almost?) all modern processors there is some form of SIMD support. This includes Intel(SSE), AMD(3DNow!), PPC/CELL(AltiVec) and so. Somehow all implementations supports the same data format: 128 bit SIMD4, which means operations on 4 operands at a time, when the total width is 128 bits.
Optimizing code for such machines from scalar code is something that can be done better off-line, not JIT. These optimizations tends to be complex. For example, see: http://portal.acm.org/citation.cfm?id=996853
Having byte-codes that will directly support SIMD, will allow to implement such optimizations at compile time, and to have better performance, specifically, but not limited to, streaming and media applications.