Couldn't you scale horizontally, e.g. with thousands of satellite base stations scattered across a continent? Then each one could occupy a separate, non-overlapping spatial channel.
Perhaps you could split up and distribute your network backbone over something like that?
That'd require scaling up either the number of satellites or their size (talking to thousands of base stations at once = more power, more antennae) dramatically.
It is possible with micromirror devices to have a single lens on a satellite to send thousands of beams in different directions.
That opens up the idea of N satellites having N^2 bandwidth... Which scales much better than optical fibers, where in general to have double the amount of bandwidth, you have double the cable laying effort.
Current starlink satellites do not have this ability - they can connect to max 3 other satellites I believe, which is pretty much the minimum for a fully connected network.
>> in general to have double the amount of bandwidth, you have double the cable laying effort.
Getting double the bandwidth just means laying a slightly thicker cable, and I do mean slightly. Adding a bundle of extra fiber when laying a cable adds maybe a millimeter to the cable width. The cost of the fiber is almost irrelevant to the cost of the other layers and the effort of placing it. Most cables are therefore laid with plenty of extra "dark" fiber for later expansion/redundancy.
Perhaps you could split up and distribute your network backbone over something like that?