For those of you who don't religiously prowl the Paradox Forums, there has been a lot of conversation going on about the new industrial districts, and the devs have been keeping engaged! Lots of communication and open discussion, which is a welcome sight after the lack of engagement many previous dev diaries have had. There are two important bits of info:

1) The Factory and Foundry building which give bonus artisans or metallurgists to industrial districts are mutually exclusive from each other. So no, you can't stack 6 jobs from one district. Ecumenopoli can build both, but the factory and foundry only effect their respective arcologies, so no double dipping.

2) The devs added in that the forge world and factory world planetary designations shift one job towards their direction. So If you want to, now you can have fully specialized worlds.

Of course, all of this is just early designs, and subject to change, so be aware systems will continue to change and evolve. If you want to read up on the dev posts and follow along, here is the link.