The justice department will not indict a sitting president. If they did the legal argument as to whether they can or not might last longer than his term, anyway.
I agree that an indictment is unlikely, though it is only Justice Department policy, not written law that prevents it. And yes, legal challenges to any indictments would likely take so long to be resolved that they would become moot. OTOH, check out this WaPo article from a few days ago:
It would be ironic if an attempt to suppress an indictment turned out to be the guarantee that a report becomes public. Three dimensional chess, anyone?