So you're thinking it'll be a complete Codex rather than just a set of extra units to add to existing imperial Codex? I like that it's always something that pops up in the fluff, with the armies of the imperium drawing from a number of sources.

The Taitor Legions book is going to have to be pretty packed with stuff there's so much to cover. I'm interested to see how the cover each Legions character especially given how the HH series has changed how some of them are characterised. The Nightlords for example aren't necessarily the super stealthy force they were portrayed as in the 3.5 Codex. I guess we could look at the FW HH series but that would add a lot of extra rules rather than using existing USRs. Of course they did add plenty of extra rules for AD Mech so who knows.

Exciting times.