Mueller is being used as the tool to drag everything on until the final HAMMER is dropped. If he were to come out now, or before now, with any 'Conclusion' it would severely alter The Plan - He must certainly was/is dirty (He brought Russia the Uranium sample for the U1 transfer & it's well documented), but now he is doing whatever POTUS needs him to.
If he falls out of line - POTUS simply exposes the conflict of interest between him, RR, & RR's wife, which would IMMEDIATELY shut down the already illegal SC (It was not created by a Law; Dig Janet Reno's involvement in 'creating' the SC) that RR & Mueller helped craft/create.
Make no mistake - RR & Mueller are POTUS' bitch now!