Just some random thoughts I've had while looking through books and considering "builds" with AoS, feel free to add your own.

Apparently units can have multiple standard bearers and/or musicians. You can't double up effects, but you can have built-in redundancy, which is nice for units with serious benefits like Skeletons. Only one leader (singular, whereas others are plural), though.

Plague Priests aren't Wizards, which means they can't act as Nurgle Wizards. But Grey Seers and Warlock Engineers *are* Chaos Wizards, so you can summon Daemons into a Skaven army. You could get a small bit of synergy between Nurgle Daemons and Pestilens Skaven, but not enough to be serious concern. Still, a Warlock Engineer summoning a Bloodthirster to do his bidding is kind of amusing.

Despite it being basically a Greater Daemon of the Horned Rat (and I think it even has the Daemon keyword), you can't summon a Verminlord. Either it arrives with you, or it's not showing up to fight today.

Speaking of summoning, you can't summon a Mortarch any more. Sure, only Nagash could do it before, but it was amusing to pile on your opponent by building up some summoning points and then dropping Mannfred on top of him, too. Okay, so maybe that explains why you can't do it any more...

Undead used to be the army that crumbled, now they're the one least likely to crumble. Battleshock of 10 for pretty much everything means you won't lose many of them to Battleshock tests. Add in the ability for standard bearers to bring back dead units, and they get more resilient. Use the battalion with a Wight King and he helps bring guys back, too. Toss in a Wight King with standard, and plant it in the middle of your army, and suddenly you have Skeletons and Grave Guard with a 6+ unmodified save on top of their armor save, so they're a bit more resilient, don't run easily, and you can just keep bringing them back. That's before you even get into using spells to add more.

Random thought: Battleshock could be shortened to its words' initials, but I don't think people want to spend their whole game taking "BS tests."

The "joke rules" weren't a short-term thing. There's still some in the Grand Alliance tomes. When I play my Nurgle Daemons (probably mixed with Skaven), I'll have to giddily "shout" the number seven at times. I think just doing it a little louder than normal voice will suffice. (Also, I'm now picturing a scene from How I Met Your Mother where Robin's being told to be "happier" and "more wry" about saying a number.)

I'm going to have to discuss with some opponents that one warscroll =/= one warscroll in some cases. For example, a Skaven weapon team is one warscroll itself, but it's only one model. If you want multiples, that's multiple scrolls, and if you want a unit and weapon team, which used to be just one unit, that's two warscrolls. A block of 25 Stormvermin and a Ratling Gun isn't exactly equal to two blocks of 30 Plaguebearers.

Speaking of Ratling Guns, why would you ever not go for the extra shots? You could get 4D6 shots with it, just with the chance you might roll a 1 and hurt the team, which might not even kill them... and if they survive, you still get 2D6 shots (since it never says they don't fire). Given that I'm used to seeing Skaven war machines go nuts, I'm quite okay with taking that chance every turn. (Once you see enough Skaven - or Orks, especially in 40K 2nd edition - blow themselves up, you learn to just laugh at it and stop worrying about it.) Pretty much ditto for any other Skaven weapon.

Yeah, that's a lot of random thoughts, but I felt like doing a "thought dump." Maybe some of those thoughts are actually useful to other people!