... or you could rely on that interference at the point of reception to form unique signals for every recevier by synthesizing waveforms from an array of transmitters, dynamically calculated based on the location of each transmitter + receiver + interference pattern. This would effectively give an unlimited number of signals within the same spectrum with no additional bandwidth (constrained only by the number of transmitters).>
MIMO techniques can be useful but they aren't as magic as you seem to think (and a nieve analysis would suggest)
In reality a couple of things limit your performance.
1: the channel estimation is nessacerally imperfect
2: the calculations needed to seperate out the virtual channels also tend to amplify the noise.
This is especially true if the antennas are close together.
This is what Artemis is now testing with their pCell tech, using a data-center of waveform-calculating servers + cheap low-power transmitters about the size and cost of a off-the-shelf wireless router:
Yeah distributed mimo has the potential for significant gains. It also has a significant cost as it needs very high bandwidth fixed line connections from the "waveform calculating servers" to the transcivers.
Be careful not to take marketing material too literally.