Surprised to see caster pet mentioned since it's really just a rehash of an idea rejected by mages (fire pet = nuker ai). But since there are apparently other threads about FC replacement now I don't mind taking over this one for the caster pet thing.
I've started work on a little caster AI just cuz and in the course of thinking about it it occurred to me that a lot of the things I was thinking about automating are best left in the player's control. CC sensitivity is the main one: rather than making the pet keep track of everything around and decide for itself whether CC is likely to happen on a target, I decided to just make the pet refuse to cast on anything before its owner tells it to attack, and to make it only cast spells on its primary target. So in other words, if something runs up and bops you at the beginning of a pull, the caster pet would just sit and watch until the moment you hit Pet Attack, rather than immediately thinking about casting a DoT on the thing that hit its master.
I'm thinking that the Pet's manapool and mana regen will scale with it's owner's, including FT and whatnot. Also will probably add mana regen and maybe some other casterly things to Ancient: Gift of Unlife. And the pet will benefit from the owner's focus effects including Mana Conservation and Casting Speed Increment, provided they have the Shared Power AA.
With most considerations left up to the Necro, the AI itself would be pretty simple. It will automatically sit to med when you let it stay still outside of combat, automatically getting up to follow you when you move and plopping back down whenever it gets the chance; it'll jump back up and inform the owner when its mana is full as well. /pet report will show its current mana ratio also.
As for combat, if the Necro has Minion Skills AA at rank 3, the pet will have 3 casting modes which the owner will be able to switch between on the fly by changing their current stance. Details here are subject to change.
Aggressive mode:
In aggressive mode the pet will do all that it can to maintain its DoT rotation, casting any DoT that will be at least 25% effective after resists. If it sees one of its DoTs is about to fade (1 tick remaining) and has nothing more important to cast in the meantime it will start to pre-cast the fading DoT. The pet will not consider using direct lifetaps to maintain its health in this mode, although a lifetap DoT is part of its DoT rotation. It will not attempt to conserve its mana in this mode either.
Normal mode:
If you don't have Minion Skills at rank 3, this will be the only available mode. In this mode it will make some attempt at keeping its health up and conserving its mana when it gets low. If the pet's HP is below 75% OR its target is in melee range and targetting the pet itself (i.e. attacking it) it will prioritize its direct lifetap spell. Otherwise, it will cast DoTs that will be at least 50% effective after resists. As its mana gets lower it will cease casting its less effective DoTs. If none of its DoTs will be at least 50% effective against its targets and it has no DoTs running, it will cast the one DoT it considers to be most effective.
Defensive mode:
Defensive mode is much like normal mode, but with more emphasis on maintaining health and conserving mana. If the pet's HP is below 50% it will prioritize a quick lifetap (Deflux). Otherwise, if its HP is below 90% or it thinks it's being attacked, it will prioritize its normal direct lifetap. Otherwise, if its HP is below 98% it will prioritize its lifetap DoT. If none of those things occur, it will cast any DoTs that will be at least 50% effective after resists, as above. However, its worst DoTs will be filtered out more quickly than in Normal mode to conserve mana. Lastly, if its HP drops below 75% and the pet is in the middle of casting something that isn't a lifetap or lifetap DoT, it will interrupts its own casting to start casting a lifetap asap.
Furthermore, the Necro will be able to interrupt its pet's casting at any time with Pet Back Off.
The exact spell lineup will need to be balanced and whatnot (and something might need to be done to make up for the lack of scaling compared to melee pets with haste and weapons) but at the moment I'm seeing it as a level 60 Necro with these spells:
Funeral Pyre of Malath (highest priority DoT)
Envenomed Bolt (second highest priority)
Vexing Mordina (middle priority except in aggressive mode)
Splurt (second lowest priority; middle priority in aggressive mode)
Plague (lowest priority)
Ancient: Lifebane
Deflux (defensive mode only)
No spells with secondary effects that might cause problems (snare, undead nuke with destroy target, stat taps, debuffs).
I'll probably make them able to proc wrist procs to give them something to make up for lack of weapon procs. And I guess just to make that explicit: the pet will not melee and will not run up to its targets unless they are out of range or out of line of sight.
Cue disappointments.
Oh one last thing, in looking up Minion Skills AA I found out that it hasn't been doing what the AA says at all in years if ever, so Necro melee pets will be getting a small corrective buff in the near future as well.