Please see http://forum.texmacs.cn/t/does-the-r-plugin-work/434/2 (you maybe have figured it out on your own). I tried the solution with R_LIBS_USER=~/.local/lib/R, and despite still an error being present it is possible to enter commands and see the output. Plots are displayed in own windows, but it may be that with simple programming they may be embedded in the document too.

Edit: in the same thread one can read how to embed plots generated with R in the TeXmacs document. So my impression is that there is sufficient functionality for working.