I used to love this idea, but when you actually think it through it's just not necessary / borderline plain dumb. Unless I am missing something, I really hope that US tax dollars are not thrown into this boondoggle.
1. This will come up on any ballistic missile radar as a threat. "Oh don't worry nuclear armed enemy, it's just cargo."
2. Unless it's a one-way trip, this would require huge infrastructure investment for "stage zero" and for logistics required for the oxygen and methane tank farms at both ends.
3. The trajectory is much more predictable than the flight path of say a C-17. This would greatly simplify interception.
4. The landing options are hugely limited compared to say a C-17. There is no go-around option. LZ got hot during transit? Too bad, we are landing!
5. I cannot identify the type of cargo that would be better served by the least stealthy delivery method possible, and most fragile landing infrastructure, only to save a dozen or so hours of transit time. Prepositioning the cargo closer to potential trouble zones and using traditional aircraft seems to be a much better idea in all cases that I can imagine.