I think R should be natively integrated to R. Just like JDK, we should enter R path and use it natively in Calc. There should be at least an R script framework.
I may help community to develop such a feature, but I am not a good programmer.
please go to IRC channel #libreoffice-dev on freenode.net and say our developers about your desire to develop it.
or write in to mailing list Development/Mailing List - The Document Foundation Wiki