For how long will I need to diverge from develop? A few weeks make sense but a few months doesn't. This prevents me from enjoying bug fixes, feature requests, and being a part of IMP development in general.
Perhaps it is part of the price o using develop, but it sounds not right to me that the nightly build of IMP will not even allow an option of producing RMFs that can be visualized. Why not keep supporting both the old and new lib for a while (like eg Word 2007 backward support).
For chimera, I'm think sure you either need to wait until chimera gets updated or stick with the old lib. I'm pretty sure there is no way to hack up some hybrid (other than, perhaps, but not writing data of the types that chimera complains about). I'm really not seeing what the benefit is to using the updated IMP and npc in the meantime. What are you trying to accomplish?