Mekanism require CoFH core installled for order to use RF, but it's totally wrong. Dependency annotation (like @Method(modid = "CoFHCore")) and possible some other parts should migrate to CoFHCore|energy api container, so this allow to use RF without CoFHCore installed, for example transport energy from/to Mekanism to/from EnderIO or any other RF mod.

This is already reported and planned.