Just to clarify this is not regular multi-mode fiber, but a single fiber with seven cores.
A singlemode fiber is limited to about 100 Tbps per fiber at 10 bits/s/Hz. It is not obvious to me how much bandwidth usage has to grow until it becomes more economical to deploy this new kind of fiber rather than multiple (existing) singlemode fibers. For example, for high bandwidth applications MPO connectors with 12 or 24 fibers per connectors are used.
I'm curious as to where you came up with your symbol rate numbers. The theoretical limit[1] is 2 bits/Hz which for infrared light (~400THz) would put the limit at ~800Tbps.
The usable parts of infrared light (amplifiable C and L bands in single mode fiber) is about 10 Thz. According to Shannon's theorem the theoretical upper limit for symbol rate in a linear channel with 30db SNR is 10 bits/s/Hz, independent of modulation format. This is how I derived my rough estimate of the capacity of single mode fiber.
The Nyquist rate is modulation dependent. Optical fiber can certainly achieve spectral efficiency over 2 bits/s/Hz.
A singlemode fiber is limited to about 100 Tbps per fiber at 10 bits/s/Hz. It is not obvious to me how much bandwidth usage has to grow until it becomes more economical to deploy this new kind of fiber rather than multiple (existing) singlemode fibers. For example, for high bandwidth applications MPO connectors with 12 or 24 fibers per connectors are used.