Android 4.4 has been announced and brings an interesting new feature: Renderscript Compute is now accessible from the NDK from C++ code. There is very little documentation atm, or at least I haven’t found it but you should download NDK r9b at the time of writing to see a HelloComputeNDK sample in the samples folder. It looks like a fully native solution, i.e. you do not need to write any Java code to access it afaik. The Android 4.4 release notes say that you should be able to access all renderscript functionality including intrinsics and user-defined kernels from the NDK. This is quite a nice development and kudos to the Renderscript team, but they do desperately need to address other concerns such as documentation. I still do think that they need to provide access to a lower-level API, such as OpenCL, to complement the high-level Renderscript. But I guess such is life.
As an aside, release notes also say that Android 4.4 enables GPU acceleration of Renderscript (I am assuming only for Filterscript) for all recent Nexus devices (Nexus 4, Nexus 5, Nexus 10, Nexus 7 2013) with the exception of Tegra 3 powered Nexus 7 2012, which has an ancient GPU architecture.