From an announcement from the QGIS mailing list: RQGIS has released a new version of RQGIS! RQGIS establishes an interface between R and QGIS, i.e. it allows the user to access the QGIS geoalgorithms from within R. With the new release, it is possible to run the most recent QGIS releases (>=2.18.2) with RQGIS.
RQGIS establishes an interface between R and QGIS, i.e. it allows the user to access QGIS functionalities from within R. It thus serves a similar goal as rgrass7 which provides an interface between R and GRASS GIS and rsaga, which provides access to geocomputing and terrain analysis functions of SAGA GIS from within R.
RQGIS provides access to all functions available through QGIS’s processing framework, which includes among others GRASS GIS and SAGA GIS (others are GDAL, the Orfeo Toolbox, TauDEM and tools for LiDAR data). Thus, RQGIS RQGIS offers an (partial) replacement of rgrass7 and rsaga packages. However, note that the latter two packages offer various other advantages.
I personally find rgrass7 and rsaga great tools that allow easy access to respectively GRASS and SAGA. I have less experience with RQGIS, but I can already tell that what I particularly like about RQGIS is that it makes it easier to combined different tools in an unified interface (which is of course the same reason I like the processing toolbox in QGIS). Take for example the find_algorithms function. This allows you to search for algorithms across all available toolboxes using keywords, similar to the search box in the processing toolbox in QGIS itself. I will certainly explore this package more!