My only problem with Assassinate is that it forbids any multiclassing. Assassin tree would be buffed if you could make viable 18/2, 16/2/2, 16/4, etc. builds that are centered around Assassin tree, and adding DC to the 18 and 20 cores doesn't help this. At the moment, the huge cost to multi-classing is the biggest problem with the tree IMO.

I would much rather see something like an increase in the base DC (i.e. from 10 to 12) or giving Assassinate DC to Rogue past lives. The close-to-max DC is only needed in a very small amount of content anyway, something that undergeared, first life Assassins shouldn't concern themselves too much with.