i dont think that such split, which leads to creation of new power systems can be a good thing.Indeed, MJ changes seem to be splitting the modding scene. It may or may not be a good thing. Time will tell.
If we can store RF, and then convert RF into MJ, then that is in effect storing MJ. You just won't be able to store MJ directly. I've never needed all the power that a single boiler could output, so from my perspective, I doubt I'd miss using MJ engines. I guess people more people will store steam in tanks to act as a buffer now.
depending on how RF(what it stands for again?) behaves, it might be easier to just burn fuels directly in different types of engines to produce different types of power at once.