Horus Heresy 3rd Edition: What Will Be Moved to Expanded Units?

Legacy Units. Expanded Units. Non-Core Units.

Call them what you like, but they've been a feature for a long time. 

The first time that I genuinely took note of the movement toward such non-core units was when the Caestus Assault Ram was no longer sold by Forge World. At that point, I did wonder about what people might do to purchase them. There's clearly a reasonable second hand market on eBay, and I would wager that 3D printing can help out (but I have never looked as I don't own a printer). Yet it is the first unit that I think of when considering those Legacies. 

Although I am quite certain that the Caestus will make it into the new pdf release, I am left wondering what may or may not be transferred across from the core rule book into those pdf releases. I realise we already have some shape of that from seeing the contents pages leak for the Libers for the new books. But I'm equally conscious that we've not seen everything yet. 

I also wonder if the pdf booklets will include the unusual armaments that we've become accustomed to else where (like those melta guns on Mor Deythan) or whether we really will be stuck with un-usable conversions in all of our armies. The community - at least to my mind - really flourishes with conversions and bespoke miniatures that I frankly love to see on the tabletop. So many great conversations about conversions and paint jobs whenever I have managed to get to tournaments ensue, and I really want that aspect to continue strongly. But I remain very concerned about how Games Workshop / Warhammer will attend to these notable deficiencies. I remain convinced that power fists on Tartaros terminators will be a day 1 FAQ or similar. But what else will be? And what will be relegated like the Caestus ultimately. My Black Shields plans hang by a thread!