- the possibility to open packages for compilers not installed, and extract files from those packages. Needed for e.g. mB users that want to use mP libraries and vice versa. Of course "install package" should be disabled in these cases.
I'm not sure blocking package installation is necessary. Actually, possibility to install packages to compilers other than the one the package was prepared for could save library designer some work. Assuming all needed mcl files are present in package, there's no difference in their operation in mB and mP (some mP/mB libs may even work in mC).
Presently one always has to prepare separate packages for separate compilers, even for libs that contain only mcl files
A warning that package was prepared for uninstalled compiler should be enough - next step could be an option to install the package in any compiler present, or simply to unpack it to indicated directory.