Yes it is canon, that should not change. The DGP material is some of the best Traveller material ever produced, that cannot change. I wish it was available. I wish the unfinished material, even in it's unfinished form, was available--especially titles like The Black Duke, and Manhunt.
Agreed on this, and I'd like to see the announced1 Psionic Races (Zhodany and Droyne) and Strange Races (K'kree and Hivers) AM published, even in unfinished forms (as you say about The Black Duke and Manhunt).
NOTE 1: I don't remember where I did read references about those supplements being announced, but IIRC they were planned as follow up from S&A and V&V. The names could not be exactly thise I give here, anyway
The only reason I didn't vote I'd buy it if released is that I already own most DGP material in dead tree copy.