The important thing to me is being able to make all classes while still being able to worship Nurgle, I'd dislike the idea of only having 1 class option for each god, ie Lord of Change gets Sorcs', Khorne gets Melee and Slaanesh gets Heavy Weapons (Noise Marines) type thing. I want all options available to all gods (well obviously no Sorcs' for Khorne =p)

And like the Light/Dark side thing in SW:TOR I want more visible character changes the more you align to a god. More Mutations, Armour changes, swarms of flies in Nurgle's case etc

Ya it would be cool to tell more or less what god and how devoutly someone followed from how they looked.
Would be a nice anesthetic touch.

I still do not understand why they went with undivided legions only.

Have the devs said anything about this? I can't find it if they did.

It could be to do with how they intend to do the God following traits tbh, in theory undivided need the options to follow whichever God they want, might've been tricky to have that for undivided but then have to remove it for God specific chapters perhaps?

Or perhaps they wanted to get the feel of CSM right before they added in something quite as fluffy as dedicated chapters?

Would be one sad panda if i werent a Blight Mage.

Yeh, I really want to be able to spread Nurgle's gifts from across the battle field!

I'd like to see some form of talent trees or specializations for Chaos, into the Chaos God paths. But if that is added, there should also be some form of bonus for those that are Chaos Undivided, perhaps perks of all four gods but not at the maximum.

I've never really looked into Undivided, always thought it was a bit of a rubbish way of viewing chaos myself, so not overly familiar with how it works and therefore how best to impliment it.

I'm not sure I'm a fan of the idea of being able to pick bits and bobs from the other trees, in my head it seems a bit wishy washy... I think I'd rather there was just an undivided tree that covered bits and bobs from other gods in it, in my head it just seems a tidier way of doing it.

This is mostly because I'm not sure how the Mark of Chaos Undivided would work in only having 4 trees, the other Marks, kinda make sense, if you get to the half way point in Nurgle, to go further you must attain the Mark of Nurgle, and then can't put points anywhere else, you'd then gain bonuses for having the Mark of Nurgle, and then be able to spec further down that tree etc.

But how would the Mark of Undivided work in that situation?

Well I presume you'd be able to go only up to the half of each tree, gaining only some perks but not the Marks of the specific god. Then after filling all four up to the half, I presume you could get the Mark of Undivided. But then again, that'd be too much points, so unsure how it would go.

This is the quote from the wikia.
"The Mark of Chaos Undivided is a glyph given to a follower of Chaos who devotes him or herself to all four of the Dark Gods equally. While the prayers of a mortal devoted to Chaos Undivided may be answered, they are unlikely to receive the special gifts that come from worshiping just one of the Dark Gods"

That could work, but if, as I suggested, you get say the Mark of Nurgle, for going past that mid point in the Nurgle tree, and then only being allowed to spec into Nurgle, you'd want the Mark of Chaos Undivided to be available at the same point in time - as in at the same Player Level. If you have to max out to this 'half way' point on all 4 trees before getting it, you'd be missing out on the Mark for ages...