Correct. I believe it is actually mandatory to offer ratios of between 90/10 to 50/50, but 50/50 to 10/90 is discrentionary.
I guess it is Mandatory/Discretionary that the vendor offers those ratios to the telco. Not that the telco offers any choice to the end user.
The current use of FDD requires that every user on a cabinet has the same FDD split (ie same bandplan), to avoid near-end crosstalk.
G.Fast will therefore require that every line has the same TDD split, for the same reason.
However, I vaguely recall that the standards were also going to include something that allowed the ratio to be adapted on the fly, based on demand. I have no idea whether that has to take account of the demand from all lines, and adapt all lines simultaneously, or whether they've figured out how to reduce the near-end crosstalk.
