No, really it's a question of resources: we know there are great opportunities in other platforms, from Maya to Sketchup or Modo, and would be great to write plugins for them. But we are a small company, and we employ all our time to the Max plugins (including to provide support for them).
Also both Forest and RailClone are very complex plugins, with thousands of lines of code that depend of Max. Although possible, it would be very complex to adapt our software to other 3D packages.