We are starting a cross-platform project to be deployed to Android and iOS. Obviously, a lot of code is to be shared between the two, and some of the code relies heavily on
I know this is an old question, but it appears that Portable Class Library (PCL) support was added to Mono in version 3.0.x, see the Release Notes for details, particularly version 3.0.8 :
Added PCL support to xbuild, mono’s MSBuild implementation.