Will it just improve downstream sync, or will it help upstream as well?
I assume it is transmitter end driven and only on downstream. Or will it be smart enough to cancel crosstalk on upstream too?
The DSLAM pre-equalises the downstream, it applies noise cancellation before transmitting, and post-equalises the upstream, applies noise cancellation after receiving the signal.
Upstream is actually easier than down - on downstream the DSLAM has to rely on telemetry from the modems for information on disturbers as they see the crosstalk / noise on the received signal, while on upstream it has no need as it sees the result of noise + signal.