I was thinking the same thing -- this is what RF digital comms engineers have done for many decades. The cleverness of their technique appears to be the generation of a perfect "picket fence" of rectangular spectra in the frequency domain -- which inherently results in raised cosine pulses in the time domain. I have to agree with the comment from the researcher, that it's hard to believe nobody thought of this before.
If I read this correctly, the idea of shaping the optical symbols to cram as many symbols/sec as possible is what RF engineers have done for a long time. Using smooth shapes, a typical example being the "raised cosine curve," you can reduce the bandwidth of the medium, for any given data carrying capacity.
Increasing bandwidth with a transmitter change will be great for the industry. Not having to replace the optical medium could be an easy upgrade path for existing deployments. Thanks for the work and learning.