Regarding rectangular AoE Spells still stacking.

[Bounty]

warlock player here.
warlocks have a ton going for them aside from wall of perilous memes stacking. IMO they should not stack, its still an amazing spell even if they do not stack.
no saving throw, no spell resistance check and half of it is magic damage so unmitigateable by 99% of enemies. you could still make use of multiple of them,
to cover a large area or line them up and kite mobs through it.

that being said, i do not think its a big issue if wall spells stack.
Its not like AoEs that kill anything they come in contact with is unique to warlock.
A warmage or even sorcerer/wizard, wield equal if not greater destructive power.
And for the matter of PvP... if you run into a very obvious small area AoE, that a warlock spend 2 minutes casting flame walls at, thats kinda on you^^

TLDR: IMO wall spells should not stack, buts its not a big issue if they do.

[Profezzor_Darke]

Also it it's not meta if a Barbarian (or any other class) takes the risk to jump through a wall of fire. It's a conscious decision to evaluate how hardy you are vs how hot that fire should be. And yeah, if I cancel AoE stacking, then it should account for all AoE effects.

[EO]

While we would prefer they not stack, there's no efficient way at the moment to check if they stack or not, unlike circular AoE's.