CRAN releases of sp, rgdal and rgeos

I too use R on a mac but I cannot get rgdal to use proj5 (port info proj).
rgdal still uses proj4 even when there is a newer version of proj already
on my computer.  Neither of these proj packages (proj4 or proj) use
pkg-config mechanism even though there are proj.pc files in both versions
of the package.  Maybe using the pkg-config mechanism to detect version of
packages during source installation might help?  I don't know whether this
is a "proj" or a "macports" issue though.

Neither sp/rgdal nor sf plan to accomodate the proj.h interface until the 
GDAL barn-raising project is completed. Even then, most software using 
proj will have to support the proj_api.h and the proj.h APIs because many 
platforms are bound to move at the speed of the slowest package using 
proj. The proj_api.h API does use the new mechanisms internally, but it 
isn't obvious how or whether proj.h pipelines should be exposed (GRASS has 
a prototype implementation).

If you work in geodetics and need sub-cm precision, this may matter; in 
which case please follow the GDAL barn-raising project and provide use 
cases where the proj.h API is required. The main difference is that the 
proj_api.h API always transforms to the WGS84 datum first then transforms 
to the target datum (many to one then one to many). When this was chosen 
1984 was not so long ago; the new proj.h API suggests transforming along a 
pipeline from source to target datum without going through WGS84 (many to 
many).

If your question is about how to install rgdal from source on OSX, you may 
need to ensure that you only have one version of proj installed, or use 
configure arguments and load path modifications on your own 
responsibility.