I'm not up to speed on ZBLAN at all (had to google what it is just now), but if it can really do 0.05dB/km at 1550nm [1], then it seems like it's actually ideally suited for long distance telecom. This is like taking an off-the-shelf "80km" SFP, and turning it into an "800km" SFP. Am I missing something?

1: https://en.wikipedia.org/wiki/ZBLAN#/media/File:Zblan_transm...