Turbine, I don't know about the GE9X, but you can transport a GE90 (or GEnx) in a 747F - the catch being you need to remove the fan module and ship it as two pieces. That's actually fairly easy with a GEnx due to the modular design, somewhat more involved with a GE90.
Boeing looked at making the Large Cargo Freighter - aka the 'Dreamlifter' - available 'for hire' for transporting outsized cargo. Two things killed that - first off it would have complicated the certification and operation of the LCF relative to having it dedicated to moving 787 bits (read more time and money). However the real show stopper was that the four LCFs are already booked pretty solid simply supporting 787 production. In fact, if one gets pranged (or worse) and is out of service for any length of time, it'll affect the 787 production rate.
I was in a meeting many moons ago where it was proposed that they contract to build a fifth LCF while the tooling and expertise was still available - where it was pointed out that only have four would be seriously limiting (especially if one got damaged). They got turned down because upper management didn't want to spend the money.