I should mention that the only problem we have this approach is that neither the AST structure nor the plugin API is guaranteed to be stable between releases, s

I should mention that the only problem we have this approach is that neither the AST structure nor the plugin API is guaranteed to be stable between releases, so if you want to use Renjin's full tool chain, you have to be able to install a copy of GCC 4.6.x locally, which only gets more difficult over time. This is the actual point of debate: RMS wants to keep these APIs moving targets in order to discourage Intel or whoever from writing a compiler that just shells out to gcc to handle all of the parsing. Unfortunately, fully GPL'd, open-sourced projects like our own (and who knows how many others that were never even started because of these artificial hurdles) are the ones most affected.