[2020] Dev Diary: Thralls in the night

The Ancients were placeholders til we built the Thrall NPC's. Thralls are specifically for Majors, minors/exploration still come from where they currently do in 5.100.
Thralls do "inhabit" the upper end stations in .110.

White Disciplines will continue to be available from vendors in .110 as they are intended for people to try out builds and experiment.

Yes you can no longer upgrade White quality vendor disciplines via the combine mechanic.
Thralls all drop Blue quality and you combine multiples of 3 disciplines / 3 essences for upgrade stages.

Pretty sure I saw The Blacksmith thrall running around! Harvesting soul gems will continue to come from harvesting.

The +15% is a bug that exists in .100 that has already been fixed for .110.
You threw this out there as kind of a snide remark and I want to drill down into it for a second; "Or no benefit just forced PVE to collect appropriate souls?"
Understand that almost all of the content activities we put in game are there to pull and push players into areas where they can encounter other players. For example the purpose in having items on vendors that cost lots of gold is to make players gather gold. The most lucrative places to gather gold are from level 30 NPC's or selling crafted goods to players. In order to get to level 30 NPC's or decent resources, players need to head out into a world that has limited amount of NPC's and resources. Players sitting in a level 30 adventure area either drove off other players or are going to get jumped by other players at some point.

Having players always wanting and on the lookout for Thralls (because it takes multiple soul gems to upgrade past rare quality, all Thralls should always have value to everyone) is going to create a window of time (night) where people are out in the world looking for Thralls. This gets people out of the bases, and creates opportunity for PvP.
You are going to see that with most of the .110 content now that we have the tools and the zones to support it!