Banish used to be a much better spell in W3ft, back before it was introduced to WoW.
I understand that Banish can only be used on demons and elementals but it wasn't always this way, back in pre-wow; banish could be cast on anything that wasn't immune to spells it could even be cast on yourself, it was so much more useful back then.
Casting banish on yourself renders the caster immune to physical damage but unable to cast spells...that could be quite useful in PvP and PVE.
I really think bringing the old banish back and introducing it as a new and improved warlock spell would do wonders for locks trying to fight off rogues and warriors it could even be a way to get out of combat when needed to in a PVE/leveling situation, it could be the equivalent to a Paladin's Shield, a mage's invisibility, hunter's feign death(Not so much but in a way) and a rogue's vanish(I think it would definitely make banish a more frequently used spell since we rarely get to Banish anything in raids anymore.)
Yes i do realize that we already have Demonic Teleportation but i do think that a spell like Banish *New* could a nice fun (Isnt that what blizz is going for^^?) addition to the warlock's currant spells, and yes i do realize that such a spell would be overpowered and would make killing a warlock too much of a hassle maybe if it had something like a double cooldown as long as you keep casting it on demons and elementals it's cooldown would remain 0 seconds while when casted at self it automatically changes the cooldown to something more balanced like a 1-3 minute cooldown or maybe you could even burn a shard to empower your banish to giving you the ability to cast it on yourself.
[Banish]*W3FT*:Turns a unit ethereal and slows its movement speed by 50% for 18 seconds(at level 3).Ethereal units cannot attack, but they can cast spells and will take 66% more damage from magic attacks(Obviously we need to get rid of that) and spells.
This is just a fun thought that I wanted to share, i may be wrong about this, or you could always do something fun with ''Enslave Demon''.