Here's what i think:

Nightmare vs Hell XP rate (not drops):
Would make leveling way to easy, imo its allready easy to get a lvl 80 in a few hell cow runs ( spectate helps with this ). I mean there's allways some public games up, where u can spectate for some exp. It would make leveling to 99 even more easy, if people open inferno cows in Nightmare ( killing even faster, while gaining the same exp ). Not even mentioning this for using it in a Ladder Reset. My advice for someone who's new and doesnt get help and has to go trough it solo, pick up rares it helps alot! ( Knowing the community we have, there's allways people who rush and help people out. We have a awesome community!

Azathoth organ drop rate:
Theye all have the same droprate from what ive been told, its all about luck here.

Potions upon Death:
I figure alex would have a hard time implenting something like this, because when u die u have no belt, hence u lose the extra slot u normally have from the belt. ( Maybe Alex could make it so u have standard 4x4, without a belt? ) Neat idea if possible!

Runeword Skill variables:
I think, using ur examples, its allready hard enough to create a perfect 6 bo or perf aura weapon/item. It would also make low rolled runewords not have any value at all, lets say u roll a cta 1 bo when 9 is perfect. The difference is way to high!

Thats what i think about it