Although I've not yet played 8th the guard (or anything for that matter) I think I've seen enough to know where they need improvement. I hope that isn't too arrogant.
First of all, the psychic powers and Wyrdvane Pyskers. The former are OK, but the latter are still poor. So here's my suggestion:
Psychic Barrier: Change it to "all friendly Astra Militarum units within 6" of the caster gain +1 to their save". Now, Wyrdvane Pyskers have a way to protect themselves while still being useful to the army as a whole. I think the Warp Charge might need upped in this case though.
Wyrdvane Pyskers: First, change their
WS to 4+, and give them a 5+ save. Let them match regular
IG infantry at least. Then there's Choir Of Minds. I was trying many things, and I think that the current system (1D6 with +1 for 3+ models and +2 for 6+ models) works OK. I tried 1D6 + total number of models in unit but that's too good. Here's my only suggestion to boost it; if the roll for casting Smite is 7+, it inflicts
D6 mortal wounds instead. So now, your Wyrdvanes can function as portable cover or a sort of artillery weapon. Hopefully these changes make them useful without being
OP. But I am prepared to bump up their price. What do you think?
I'm also looking at Leman Russes, but only once the Psykers are fixed.