So I've done some testing. And editing in accordance with the results of the testing.
I've added some things: ore that can be smelted into mithril (with luck), more uses for mithril, some 'rebalance' (dark iron and fungal steel aren't supermetals anymore). Also, I've added some features from the Orichalcum mod: new glazes (including uranium glaze!), new sources of porcelain, and lead crystal.
The main addition this time is the (yet another) rewrite of the Rainbow Factory. Spectra and rainbows are not metal bars anymore; they're extracted and mixed as liquids (OMFG !!canon!!), and used in reactions as liquids. To create furniture, rainbows have to be combined with synneplast first in order to solidify them.
I'm going to test this build until the game update arrives, hopefully with functional plants in it.